royong
19-04-2006, 16:49
Disclaimer ::
This has been ported from my old 74r.Com web site.
Information and viewpoints may be dated.
Being a fan of Linux based web servers and having devoted numerous hours in research and readings to find out how they are deployed, I have been asked on a number of occasions to provide information and suggestions as to how, what and where to set up a web server. My answers were mostly informal and threaded on different aspects of a web server, dealing with issues that were most familiar to me at that time. I have, at last, been able to devote sufficient time and effort to put together an article that, in my opinion, would address most of the key issues.
Disclaimer :: This article has been primed to focus on the needs to set up a web server in a local Data Centre for purposes of being a Web Host Provider, on a commercial basis or as a web server, purely for leisure purposes. I have used these key considerations myself and for my customers but would like to re-iterate that these are solely my personal viewpoints and each individual reader is entitled to conger his own judgement.
1. Introduction
Web Servers, as they are commonly referred to, are really a piece of equipment that providers combination of multiple server services. For most, it consists of the following services :-
(a) Main Operating System : Red Hat Linux
(b) Web Server : Apache
(c) Domain Name Server : BIND
(d) File Transfer Protocol Server : ProFTP / WU-FTP
(e) Mail Transfer Agent : SendMail
(f) Firewall : IPTables
(g) Routing Capabilities : IPTables
(h) Database Server : MySQL
2. Hardware Considerations
Building a server from scratch can be a daunting task. As such, for the faint hearted and non-technical users, a simple call or a browse through catalogues would be the best option. Brand names such as Dell, Hewlett Packard, Compaq etc have wonderful server built for every need and size. However, this doesn't seem to satisfy the gutsy individual whom is stubbornly insisting on building their own. For those, here are my suggestions.
:: Set yourself a budget
With ever-growing competition, the next better upgrade is only a few dollars away. Bear in mind that a few dollars here and there will ultimately lead to quite a hefty sum. My advice, set yourself a budget and stick to it. Be prudent with your first server !
:: Random Access Memory (RAM)
Purchase as much RAM as you can afford. With RAM prices at rock bottom, the minimum purchase should be a stick of 512MB. If at all possible, 1024MB would be ideal.
*My recommendation -> Kingston SD or DD Ram Modules
:: Hard Disk
In my opinion, this is the single most important component of the server as it houses not only the operating system but all the data as well. However, true to popular belief and my own personal experience, it is also the component with the highest rate of failure. As such, I would recommend that sufficient funds be set aside for the purchase of at least 2 hard disks or if at all possible, the purchase of 3 hard disks.A suggested deployment scheme could be as follows :-
Hard Disk A and B to be deployed in as software RAID 1 while Hard Disk C could be used as a backup hard disk either on the sever itself or via remote backup capabilities.
Personally, I never deploy web servers with less than a software RAID 1 partition and I recommend all my customers to do that same. With RAID 1 capabilities onboard, I feel more confident in maintaining a high level of uptime. A single drive failure will not render my server useless and with that comes a price paid in terms of a slight loss in overall system performance, but I feel that such a tradeoff is definitely worth the price. For my deployments, the 3rd hard disk acts as a remote backup solution where at least I can remain confident that the customers' data is safe in a remote location.
*My recommendation -> Western Digital 80GB (8MB Cache)
:: Casing
When choosing a casing, the first point to note is the overall volume of the casing. When you are ready to collocate your server in a datacenter, the provider will bill you in accordance to the thickness of your server. In summary, the smaller the server, the less the charge. Casing is simply a single box that houses all the components in a compact unit. However, bearing in mind that the web server is to be in operation 24x7, please take some time to search for a suitable casing which not only would be able to house the motherboard, hard disk etc but would also promote good airflow and ventilation. Although a 1U casing is commonly recommended for web servers, so as to save on collocation costs, I strongly feel that current OEM 1U casings are lacking in airflow design. As such, my recommendation would be to go for a 2U casing so as to promote heat dissipation. Here's a little secret, you may want to look at BookPC cases - some of them provide for good airflow in a small nifty little box. Then again, you'll have to check with the provider of the collocation if at all these casings can be used.
:: Motherboard & CPU Chip
The final piece to the hardware jigsaw would be the brains to the server - the motherboard and the CPU chip. I'm not an expert in this area but having read quite widely on the topic, I personally place more emphasis on reliability and the overall lifespan of the motherboard and chip. With the consideration of 24x7 operations, this bears extreme importance. After some testing, which includes 2 burnt chips and a damaged motherboard, I have to say that one has to avoid the AMD Duron chips at all costs. They seem to have a slight problem in disseminating the heat generated in a small tight space but anyhow, this is just my own judgment and findings, you are free to disagree. For me, preference for AMD lies in the XP1800 and XP2000 chips. These little babies are relatively inexpensive and provides for sufficient processing power to drive a web server. On the other hand, an Intel lover would be inclined to look at the Pentium 4 1.8 to 2.0 Ghz series of chips. On the issue of motherboards, I have a particular likely for MSI and Gigabyte motherboards simply because in the recently times, their designs and particular attention to reliability, has made me an avid fan. As a side note, please bear in mind the casing that has been chosen. Based on the limitation of space, you might be forced to look for a motherboard that has a host of components already onboard as the casing might not be able to accommodate add-on cards. Of extreme importance is the VGA connector and the LAN connector although these have become very much the standard on combo boards.
*My recommendation -> AMD XP1800 or Intel Pentium 4 1.8Ghz CPU Chips
*My recommendation -> MSI or Gigabyte Motherboards
2. Control Panel
The main uses of a control panel is to facilitate ease of use. A well-trained server administrator should be able to handle all or most requests made by the customer without the use of the control panel. Instead, these could be carried out via commands on the command line, otherwise also commonly referred to as "doing things by hand". However, the commercialization of the web hosting industry has lead to an influx of web hosting control panels where the customer is no longer tied into requesting for support from the web host provider every time a small change is required. With the web hosting control panel, the customer would be able to carry a limited variety of changes and additions on his own, at his own leisure, in a secure environment, without any intervention from the provider. Current popular web hosting control panels include : H-Sphere, Plesk, CPanel, Ensim, Web://CP, WebMin & Usermin. Of these, my familiarity lies with CPanel and Ensim, of which some avid fans have said to have dominated the web hosting control panel industry.
:: CPanel
CPanel comes in a 2 module system where the end user i.e the customer uses a module called CPanel to carry tasks which solely pertains to his domain. On the other, the web server administrator and reseller alike, use a more featured module called WHM (Web Host Manager) which includes support to edit all domains within the administrator's or reseller's control. The initial plus factor in the deployment of CPanel is in its superior user-friendliness and the ability to be "skinned" and to customize the control panel to your liking. Another plus point to the deployment of CPanel is the ability to check back with the license providers, on a nightly basis, for any updates thereby minimizing server administration tasks. License costs for one-time purchase is pegged at a hefty US$1,400 per server although most CPanel deployments ride on the monthly licensing scheme where payments of between US$40 to US$85 per month are levied.
Having related most of the advantages of CPanel, would it be my choice of web hosting control panel ? Unfortunately, no. In sharp contrast, I find that CPanel server administrators lack control on the server. The users are empowered with too many features which could lead to more support calls as the users come to grip with all the features made available. Also of major concern is the auto-update feature - this, in my opinion, poses more as a thread then a solution. As a server administrator, I crave for control and the very fact that my server could be risking failure because of a major screw-up in a faulty update certainly scares me and does not reflect well in my efforts to main high reliability and high uptimes. The last issue that completely freaks me out is the sheer number of reported hacks and server compromises. A simple Google on this subject matter freaks me out rather badly.
:: Ensim
Ensim, many non-users say that this is the ugliest control panel available in the market. I would tend to agree to a certain extent especially the work that has been done on Ensim Webppliance for Linux 3.1.x However, with the recent upgrade package announced to Ensim Webppliance PRO for Linux 3.5.x, the overall interface as improved a great deal. However, as compared to CPanel, it still lags behind the latter. The plus point for Ensim, is the fact that only the essentials are provided to the end-user and it does not awe them with fanciful features. Also of great relief is the emphasis of server security by its deployment of "jailed" accounts where each account is only allowed to roam within its own space, not being able to see the files of others. (Surprising, this is a feature lacking in CPanel, where users could see each other's files although access to them is restricted.) Adding to the emphasis of security is the deployment of 4 levels of access, namely, Appliance Administrator, Reseller, Site Administrator and User. The restrictive nature of the control panel clearly surrogates the accessibility of the various levels to good effect. Updates are to be carried out manually giving the server administrator more control of the server. Licensing costs are varied based on number of domains in which a server is limited to. More information can be found at its official web site http://www.ensim.com (http://www.ensim.com/)
Overall, I find Ensim a good product if you are one that does not place emphasis on the bells and whistles. Ensim is a product that clearly emphasizes on security and is one that is designed to carry out its job without all the fanciful add-ons.
3. Main Operating System
Based on the choice of control panels, one will have adhere to the requirements of control panel. Ensim Webppliance PRO for Linux 3.5.x currently only runs on Red Hat Linux 7.3 and is somewhat restrictive in this area. CPanel on the other hand can run on a variety of distributions and work is constantly being carried out to roll out support for more distributions. Naturally, as with any product, support for a newer release is always more desirable.
4. Collocation Provider / Data Centre
Now you that have your server assembled, setup and configured, its time to roll it off to the Data Centre (DC) for collocation. The only problem is, which DC ? In Singapore, we are blessed with fact that all DCs are accessible and are usually less than a 30 minute drive away. Choosing a DC close to you is only one factor in determining the overall choice of a DC. Typically, my advice to web host providers would be to consider the requirement of bandwidth as top priority. In many local DCs, bandwidth used per month, as in the amount of data transferred per month is unlimited and uncapped. However, what is capped is the pipe that connects your server to the internet. Based on the relative size and bandwidth made available to the DC as a whole, your allocated pipe could be as little as 64K or as large as 10Mbps. Although there are no written rules with regards to the actual amount of data transferred, local DCs have been seen to politely request server owners, using excessive bandwidth, to upgrade and purchase a fixed block of bandwidth themselves.
With this in mind, the hunt for a suitable DC begins. As you will quickly realize, most DCs only rent out server space by the racks - not by the number of Us as required by your server. As such, you are now forced to look for a collocation reseller, whom is one that purchases an entire rack from the DC and then resells the rack space in smaller chunks as required. However, before determining a reseller, you must already have a DC in mind, to which you will house your server. Here's a sample list of the DCs that are located locally.
(a) Singnet Data Centre http://www.singnet.com.sg (http://www.singnet.com.sg/)
(b) Pacific Net Data Centre http://www.pacific.net.sg (http://www.pacific.net.sg/)
(c) Starhub Data Centre http://www.starhub.com.sg (http://www.starhub.com.sg/)
(d) DataOne Asia Pte Ltd http://www.d1asia.com (http://www.d1asia.com/)
(e) LGA International Pte Ltd http://www.lga.com.sg (http://www.lga.com.sg/)
(f) Qala Singapore Pte Ltd http://www.qala.com.sg (http://www.qala.com.sg/)
(g) GWNnet http://www.gwnnet.net (http://www.gwnnet.net/)
(h) InforServe http://www.infoserve-group.com (http://www.infoserve-group.com/)
Clearly, this isn't a complete list of DCs in Singapore but is only a sample listing. As with every DC, the requirements and bandwidth availability is different. You are advised to check these out proactively as the lack of available bandwidth could result in slowed response from the server. Once a decision has been made with regards to the choice of DC, you can now safely proceed to look for a reseller that will resell you only the space required. Please bear in mind that you will need to confirm that the collocation space will entitle you to 1 unit of power socket, 1 network port connection, 2 IP addresses and any other features that the provider might add-on e.g remote monitoring, server reboots, server visits etc.
Some other areas of consideration when choosing a DC and a reseller include :-
(a) Data Centre operation hours. Some DCs may only be manned at specific times. This could prove to be a hindrance if you are to carry out upgrades, troubleshooting, maintenance etc only to find out that the DC is closed and is inaccessible.
(b) Reputation of the reseller that you are purchasing from. As the reseller is the recognized owner of the server rack at the DC, you are unable to liaise with the DC directly. All interaction must be carried out with the reseller. As a side note, the reliability of the reseller is important as ultimately he is the one responsible for the payments to the DC. Imagine if, you are consistent in dealing with your payments to the reseller but the reseller isn't as prudent with his payments to the DC. What will happen if the DC decides to pull the plug on the rack ? I know it isn't fair but its a price that you will have to pay for purchasing from a reseller. As such, make sure that the reseller is of repute.
(c) Technical Support. Another key point missed by many when looking for collocation is the amount of technical support that you will have access to. Being a new server administrator, there might be occasions where a small slip-up on your part could result in disastrous consequences. In this scenario, help at hand is always important and what better way then to approach the technical personnel of your collocation provider even though this maybe a paid service. But at least, beforehand, you will need to ensure that help is available should you require it.
(d) Visitation Hours. Some resellers and DCs restrict the amount of time each server owner can visit their servers. Typically, this is set so that the server owner does not abuse the visitation and choose to visit his server for prolong periods of time. Typically, 40 hours a month is somewhat standard and would be considered acceptable.
I hope that this article serves the needs of the reader. I would personally consider this article very much work-in-progress and I will continue to update it as required. Once again, please bear in mind that all the information expressed in this article are solely my own.
This has been ported from my old 74r.Com web site.
Information and viewpoints may be dated.
Being a fan of Linux based web servers and having devoted numerous hours in research and readings to find out how they are deployed, I have been asked on a number of occasions to provide information and suggestions as to how, what and where to set up a web server. My answers were mostly informal and threaded on different aspects of a web server, dealing with issues that were most familiar to me at that time. I have, at last, been able to devote sufficient time and effort to put together an article that, in my opinion, would address most of the key issues.
Disclaimer :: This article has been primed to focus on the needs to set up a web server in a local Data Centre for purposes of being a Web Host Provider, on a commercial basis or as a web server, purely for leisure purposes. I have used these key considerations myself and for my customers but would like to re-iterate that these are solely my personal viewpoints and each individual reader is entitled to conger his own judgement.
1. Introduction
Web Servers, as they are commonly referred to, are really a piece of equipment that providers combination of multiple server services. For most, it consists of the following services :-
(a) Main Operating System : Red Hat Linux
(b) Web Server : Apache
(c) Domain Name Server : BIND
(d) File Transfer Protocol Server : ProFTP / WU-FTP
(e) Mail Transfer Agent : SendMail
(f) Firewall : IPTables
(g) Routing Capabilities : IPTables
(h) Database Server : MySQL
2. Hardware Considerations
Building a server from scratch can be a daunting task. As such, for the faint hearted and non-technical users, a simple call or a browse through catalogues would be the best option. Brand names such as Dell, Hewlett Packard, Compaq etc have wonderful server built for every need and size. However, this doesn't seem to satisfy the gutsy individual whom is stubbornly insisting on building their own. For those, here are my suggestions.
:: Set yourself a budget
With ever-growing competition, the next better upgrade is only a few dollars away. Bear in mind that a few dollars here and there will ultimately lead to quite a hefty sum. My advice, set yourself a budget and stick to it. Be prudent with your first server !
:: Random Access Memory (RAM)
Purchase as much RAM as you can afford. With RAM prices at rock bottom, the minimum purchase should be a stick of 512MB. If at all possible, 1024MB would be ideal.
*My recommendation -> Kingston SD or DD Ram Modules
:: Hard Disk
In my opinion, this is the single most important component of the server as it houses not only the operating system but all the data as well. However, true to popular belief and my own personal experience, it is also the component with the highest rate of failure. As such, I would recommend that sufficient funds be set aside for the purchase of at least 2 hard disks or if at all possible, the purchase of 3 hard disks.A suggested deployment scheme could be as follows :-
Hard Disk A and B to be deployed in as software RAID 1 while Hard Disk C could be used as a backup hard disk either on the sever itself or via remote backup capabilities.
Personally, I never deploy web servers with less than a software RAID 1 partition and I recommend all my customers to do that same. With RAID 1 capabilities onboard, I feel more confident in maintaining a high level of uptime. A single drive failure will not render my server useless and with that comes a price paid in terms of a slight loss in overall system performance, but I feel that such a tradeoff is definitely worth the price. For my deployments, the 3rd hard disk acts as a remote backup solution where at least I can remain confident that the customers' data is safe in a remote location.
*My recommendation -> Western Digital 80GB (8MB Cache)
:: Casing
When choosing a casing, the first point to note is the overall volume of the casing. When you are ready to collocate your server in a datacenter, the provider will bill you in accordance to the thickness of your server. In summary, the smaller the server, the less the charge. Casing is simply a single box that houses all the components in a compact unit. However, bearing in mind that the web server is to be in operation 24x7, please take some time to search for a suitable casing which not only would be able to house the motherboard, hard disk etc but would also promote good airflow and ventilation. Although a 1U casing is commonly recommended for web servers, so as to save on collocation costs, I strongly feel that current OEM 1U casings are lacking in airflow design. As such, my recommendation would be to go for a 2U casing so as to promote heat dissipation. Here's a little secret, you may want to look at BookPC cases - some of them provide for good airflow in a small nifty little box. Then again, you'll have to check with the provider of the collocation if at all these casings can be used.
:: Motherboard & CPU Chip
The final piece to the hardware jigsaw would be the brains to the server - the motherboard and the CPU chip. I'm not an expert in this area but having read quite widely on the topic, I personally place more emphasis on reliability and the overall lifespan of the motherboard and chip. With the consideration of 24x7 operations, this bears extreme importance. After some testing, which includes 2 burnt chips and a damaged motherboard, I have to say that one has to avoid the AMD Duron chips at all costs. They seem to have a slight problem in disseminating the heat generated in a small tight space but anyhow, this is just my own judgment and findings, you are free to disagree. For me, preference for AMD lies in the XP1800 and XP2000 chips. These little babies are relatively inexpensive and provides for sufficient processing power to drive a web server. On the other hand, an Intel lover would be inclined to look at the Pentium 4 1.8 to 2.0 Ghz series of chips. On the issue of motherboards, I have a particular likely for MSI and Gigabyte motherboards simply because in the recently times, their designs and particular attention to reliability, has made me an avid fan. As a side note, please bear in mind the casing that has been chosen. Based on the limitation of space, you might be forced to look for a motherboard that has a host of components already onboard as the casing might not be able to accommodate add-on cards. Of extreme importance is the VGA connector and the LAN connector although these have become very much the standard on combo boards.
*My recommendation -> AMD XP1800 or Intel Pentium 4 1.8Ghz CPU Chips
*My recommendation -> MSI or Gigabyte Motherboards
2. Control Panel
The main uses of a control panel is to facilitate ease of use. A well-trained server administrator should be able to handle all or most requests made by the customer without the use of the control panel. Instead, these could be carried out via commands on the command line, otherwise also commonly referred to as "doing things by hand". However, the commercialization of the web hosting industry has lead to an influx of web hosting control panels where the customer is no longer tied into requesting for support from the web host provider every time a small change is required. With the web hosting control panel, the customer would be able to carry a limited variety of changes and additions on his own, at his own leisure, in a secure environment, without any intervention from the provider. Current popular web hosting control panels include : H-Sphere, Plesk, CPanel, Ensim, Web://CP, WebMin & Usermin. Of these, my familiarity lies with CPanel and Ensim, of which some avid fans have said to have dominated the web hosting control panel industry.
:: CPanel
CPanel comes in a 2 module system where the end user i.e the customer uses a module called CPanel to carry tasks which solely pertains to his domain. On the other, the web server administrator and reseller alike, use a more featured module called WHM (Web Host Manager) which includes support to edit all domains within the administrator's or reseller's control. The initial plus factor in the deployment of CPanel is in its superior user-friendliness and the ability to be "skinned" and to customize the control panel to your liking. Another plus point to the deployment of CPanel is the ability to check back with the license providers, on a nightly basis, for any updates thereby minimizing server administration tasks. License costs for one-time purchase is pegged at a hefty US$1,400 per server although most CPanel deployments ride on the monthly licensing scheme where payments of between US$40 to US$85 per month are levied.
Having related most of the advantages of CPanel, would it be my choice of web hosting control panel ? Unfortunately, no. In sharp contrast, I find that CPanel server administrators lack control on the server. The users are empowered with too many features which could lead to more support calls as the users come to grip with all the features made available. Also of major concern is the auto-update feature - this, in my opinion, poses more as a thread then a solution. As a server administrator, I crave for control and the very fact that my server could be risking failure because of a major screw-up in a faulty update certainly scares me and does not reflect well in my efforts to main high reliability and high uptimes. The last issue that completely freaks me out is the sheer number of reported hacks and server compromises. A simple Google on this subject matter freaks me out rather badly.
:: Ensim
Ensim, many non-users say that this is the ugliest control panel available in the market. I would tend to agree to a certain extent especially the work that has been done on Ensim Webppliance for Linux 3.1.x However, with the recent upgrade package announced to Ensim Webppliance PRO for Linux 3.5.x, the overall interface as improved a great deal. However, as compared to CPanel, it still lags behind the latter. The plus point for Ensim, is the fact that only the essentials are provided to the end-user and it does not awe them with fanciful features. Also of great relief is the emphasis of server security by its deployment of "jailed" accounts where each account is only allowed to roam within its own space, not being able to see the files of others. (Surprising, this is a feature lacking in CPanel, where users could see each other's files although access to them is restricted.) Adding to the emphasis of security is the deployment of 4 levels of access, namely, Appliance Administrator, Reseller, Site Administrator and User. The restrictive nature of the control panel clearly surrogates the accessibility of the various levels to good effect. Updates are to be carried out manually giving the server administrator more control of the server. Licensing costs are varied based on number of domains in which a server is limited to. More information can be found at its official web site http://www.ensim.com (http://www.ensim.com/)
Overall, I find Ensim a good product if you are one that does not place emphasis on the bells and whistles. Ensim is a product that clearly emphasizes on security and is one that is designed to carry out its job without all the fanciful add-ons.
3. Main Operating System
Based on the choice of control panels, one will have adhere to the requirements of control panel. Ensim Webppliance PRO for Linux 3.5.x currently only runs on Red Hat Linux 7.3 and is somewhat restrictive in this area. CPanel on the other hand can run on a variety of distributions and work is constantly being carried out to roll out support for more distributions. Naturally, as with any product, support for a newer release is always more desirable.
4. Collocation Provider / Data Centre
Now you that have your server assembled, setup and configured, its time to roll it off to the Data Centre (DC) for collocation. The only problem is, which DC ? In Singapore, we are blessed with fact that all DCs are accessible and are usually less than a 30 minute drive away. Choosing a DC close to you is only one factor in determining the overall choice of a DC. Typically, my advice to web host providers would be to consider the requirement of bandwidth as top priority. In many local DCs, bandwidth used per month, as in the amount of data transferred per month is unlimited and uncapped. However, what is capped is the pipe that connects your server to the internet. Based on the relative size and bandwidth made available to the DC as a whole, your allocated pipe could be as little as 64K or as large as 10Mbps. Although there are no written rules with regards to the actual amount of data transferred, local DCs have been seen to politely request server owners, using excessive bandwidth, to upgrade and purchase a fixed block of bandwidth themselves.
With this in mind, the hunt for a suitable DC begins. As you will quickly realize, most DCs only rent out server space by the racks - not by the number of Us as required by your server. As such, you are now forced to look for a collocation reseller, whom is one that purchases an entire rack from the DC and then resells the rack space in smaller chunks as required. However, before determining a reseller, you must already have a DC in mind, to which you will house your server. Here's a sample list of the DCs that are located locally.
(a) Singnet Data Centre http://www.singnet.com.sg (http://www.singnet.com.sg/)
(b) Pacific Net Data Centre http://www.pacific.net.sg (http://www.pacific.net.sg/)
(c) Starhub Data Centre http://www.starhub.com.sg (http://www.starhub.com.sg/)
(d) DataOne Asia Pte Ltd http://www.d1asia.com (http://www.d1asia.com/)
(e) LGA International Pte Ltd http://www.lga.com.sg (http://www.lga.com.sg/)
(f) Qala Singapore Pte Ltd http://www.qala.com.sg (http://www.qala.com.sg/)
(g) GWNnet http://www.gwnnet.net (http://www.gwnnet.net/)
(h) InforServe http://www.infoserve-group.com (http://www.infoserve-group.com/)
Clearly, this isn't a complete list of DCs in Singapore but is only a sample listing. As with every DC, the requirements and bandwidth availability is different. You are advised to check these out proactively as the lack of available bandwidth could result in slowed response from the server. Once a decision has been made with regards to the choice of DC, you can now safely proceed to look for a reseller that will resell you only the space required. Please bear in mind that you will need to confirm that the collocation space will entitle you to 1 unit of power socket, 1 network port connection, 2 IP addresses and any other features that the provider might add-on e.g remote monitoring, server reboots, server visits etc.
Some other areas of consideration when choosing a DC and a reseller include :-
(a) Data Centre operation hours. Some DCs may only be manned at specific times. This could prove to be a hindrance if you are to carry out upgrades, troubleshooting, maintenance etc only to find out that the DC is closed and is inaccessible.
(b) Reputation of the reseller that you are purchasing from. As the reseller is the recognized owner of the server rack at the DC, you are unable to liaise with the DC directly. All interaction must be carried out with the reseller. As a side note, the reliability of the reseller is important as ultimately he is the one responsible for the payments to the DC. Imagine if, you are consistent in dealing with your payments to the reseller but the reseller isn't as prudent with his payments to the DC. What will happen if the DC decides to pull the plug on the rack ? I know it isn't fair but its a price that you will have to pay for purchasing from a reseller. As such, make sure that the reseller is of repute.
(c) Technical Support. Another key point missed by many when looking for collocation is the amount of technical support that you will have access to. Being a new server administrator, there might be occasions where a small slip-up on your part could result in disastrous consequences. In this scenario, help at hand is always important and what better way then to approach the technical personnel of your collocation provider even though this maybe a paid service. But at least, beforehand, you will need to ensure that help is available should you require it.
(d) Visitation Hours. Some resellers and DCs restrict the amount of time each server owner can visit their servers. Typically, this is set so that the server owner does not abuse the visitation and choose to visit his server for prolong periods of time. Typically, 40 hours a month is somewhat standard and would be considered acceptable.
I hope that this article serves the needs of the reader. I would personally consider this article very much work-in-progress and I will continue to update it as required. Once again, please bear in mind that all the information expressed in this article are solely my own.