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I am setting up a new server from scratch. It has two 160gb HDs that are set up in a RAID 1+0 for fault tolerance. This server, and two others like it, will be used for terminal services and IIS.

My question is: If there is really not going to be a ton of storage needed on these servers, should I just make it a single logical partition on this array or should I still create two logical partitions for these servers, one for the OS and the other for data? I am not sure here.

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up vote 2 down vote accepted

If you really only have two physical drives, they cannot be constructed into a RAID 1+0 set at the controller level. You need a minimum of 4 drives to create a RAID 1+0 set at the physical controller level.

With two drives, you could create a RAID 1 set, which will leave you approximately 160GB of usable storage.

This is great to help provide fault tolerance at the disk level for your server (i.e., your server will be able to survive the failure of one of the disks). However if they are both on the same controller, a controller failure will result in downtime on our server.

There are pros and cons for partitioning this into two parts as you describe. It all depends on how you want to manage your servers. It is certainly much simpler for most people to just manage (setup, backup, restore, etc.) a single partition. And splitting it will not provide you any significant benefits for performance or reliability.

On the other hand, your administration practices might make more sense to separate the RAID set into multiple partitions, with the larger one for user files. Sometimes for recovery, it is desirable to get the server up asap, and worry about the user date later. In that case, a separate partition for the OS will allow a faster recovery of the server to a running state.

I assume that you know you'll still need to perform regular backups.

The article "Introduction to RAID" will help you if you have any questions specific to RAID.

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I'm guessing they're HP servers. HP don't seem to differentiate between RAID1 and RAID1+0 (so RAID1+0 with two disks == RAID1) – Mike1980 Feb 9 '11 at 20:39
Thanks! That was the opinion I was looking for. Backups will be set on these servers after install, but I was very unsure if it was truly beneficial to separate OS and data partations out on a server that already has mirrored drives. – Tyson Navarre Feb 9 '11 at 20:40
You guessed right, they are indeed HPs you would laugh, in the controller config, it only gives you a choice between RAID 0 or RAID 1+0 – Tyson Navarre Feb 9 '11 at 20:41

My friend, you have just asked the question that has been debated from time immemorial.

You may not like the answer but "It depends." Partitioning can be quite helpful if you're running a multitude of programs, for backup purposes, storing user data on the drive, and for helping to reduce fragmentation. However, it does come at a cost of time for proper planning and the risk of improper storage balance (too much allocated to one partition and not enough on the other).

The truth is that it'll save you some hassles by not creating separate partitions but it could come at a cost of performance and ease of backup & recovery later. You have to weigh the value of speed of recovery against the benefits of minimizing your initial administration time.

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In the Windows world the old idea of putting the OS and data on separate logical drives is not used much these days and indeed there is very little justification for doing so. If you really feel a need to separate them do so using physical drives, not just partitioning. While it shouldn't affect your scenario, multiple partitions have a serious negative impact on performance, as the head assembly needs to spend much more time darting back and forth.

As Jeff said, you can't do true RAID 1+0 using only 2 drives. While you can get something that looks like it by striping and mirroring partitions that's not really the same thing. proper RAID is set up at the drive level, before the partitioning happens.

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+1 - SQL Server is about the only place I've seen drive letters used consistantly, and that's generally to support multiple physical disks, not just partitions. – Mark Henderson Feb 9 '11 at 22:22

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