Server 2008 / RAID configuration advice

Looking for good advice on partitioning and reasons behind any suggestions please.

Installing MS Server Standard 2008 R2 64 bit OS on a new Dell PE R720 server.  It currently has (7) 1TB drives, none configured on a PERC H710 RAID controller.  The device primarily will be a file server and host to Backup Exec and a media library.

The thought is RAID 1 for the OS on a 40GB or 60GB partition first, and division of the remainder potentially twice for Program Files and an additional partition for data easily excluded from backups; i.e. copies of CD or other data easily replaced.  1GB drives are larger than needed but having been dealt this hand this seems a reasonable way to go.

The remaining (5) drives would be used in a RAID 5 array.  If the controller supports it (anyone verify?), the idea of 4 drives with one fail-over spare is appealing.  I anticipate single partition use for this array though I've noted recommendations to split as well.

Best practices?  Thoughts please?
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wolfcamelConnect With a Mentor Commented:
if you aren't going to do any database or exchange work on the server raid 5 is fine.

there is a comparison of various raid types on Wikipedia that shows the read and write performance of each type.

But for a basic file server what you are suggesting sounds fine.

I also like to have a partition for data that doesn't need to get backed up, or often.

Maybe make the system partition a little larger - say 100Gb - just to be sure.
setasoujiroConnect With a Mentor Commented:
I would opt for a raid 1+0 on for the OS and put the rest in RAID5 for the data, indeed with one spare for the array.

The controller supports 0/1/5/6 as well as 10/50/60
However I don't see the benefit of partitioning the OS drive for the program files etc..
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PowerEdgeTechConnect With a Mentor IT ConsultantCommented:
The remaining (5) drives would be used in a RAID 5 array.  If the controller supports it (anyone verify?)
The controller will easily handle two virtual disks (arrays), and a RAID 5 with as many disks as the system will hold is also supported.  You can also have up to 2 hot-spares per virtual disk on the H710.  So, yes, this controller will do all you have described as wanting to do.
DavidConnect With a Mentor PresidentCommented:
The controller handles RAID6, which is profoundly better in terms of reliability and data integrity than going RAID5 + spare.   RAID5 does NOT always protect against data loss when you have a drive failure.   If you have just one bad block on surviving disks, then you lose data when you have a drive failure.

Also a rebuild could take all weekend if this is a busy machine, that also exposes you to catastrophic data loss.  RAID6 gives you two parity drives.  This is a fast controller with lots of cache.  the write performance hit going from RAID5 to RAID6 is insignificant from perspective of end-users.

Go RAID6 instead.
safebetAuthor Commented:
Thanks for the feedback, it appears I'm on target, but I remain unclear on OS partition size.

In the past I've seen Program Files located on a separate drive - perhaps this was due to the OS being stuck for example on a too small 12GB partition.

I've seen it commented that the OS partition should be smaller, obviously less than the entire available 1 TB drives provide.  100GB was suggested, and Program Files can remain on C:\, so there is no need for a separate swap file location either?  I'm okay with this, just looking for any good reason I would need to do otherwise.  I'll split (or not) the remaining ~900GB as I please then.
safebetAuthor Commented:

Just saw your comment regarding RAID6.  In planning this I see that I may have less free space available than desirable.  

Is the following a correct assessment?

RAID 5, 4 1TB drives, 1 hot spare = 3TB total
RAID 6, 4 1TB drives, 1 hot spare = 2TB total
RAID 6, 5 1TB drives, 0 hot spare = 2.5TB total

Considering that the 7th drive would otherwise be configured as a global hot spare, using all 5 drives in an active RAID6 array would not make this available to the OS RAID 1 array in the event of drive failure, correct?

This plot thickens...
PowerEdgeTechIT ConsultantCommented:
RAID 6, 5 1TB drives, 0 hot spare = 2.5TB total

This would be 3TB total.  Two-disks' worth of storage is used for parity in RAID 6 (4-disk = 2xGB, 6-disk = 4xGB, etc.).  RAID 6 is practically using a hot-spare that does not have to wait for a disk to fail to protect the RAID - it is actively participating and protecting the array at all times.
safebetAuthor Commented:
Thank you, I see the error in my math.

"it is actively participating and protecting the array at all times" is of benefit for sure, but the downside is that it becomes unavailable as a RAID 1 hot spare drive.  Hmmm...
PowerEdgeTechIT ConsultantCommented:
There is no free lunch, obviously.  What is more important, to save a few dollars on disk; or to not risk partial data loss in event of a single drive failure; or to not risk 100% data loss if a drive fails during a rebuild.

If the data worth more than a few hundred dollars, then you know what the correct answer is going to be.
safebetAuthor Commented:
Thanks to all.  To be fair I split points evenly, each of you offered timely and relevant guidance.

I won't concern myself with special OS related partitions but will allow ample drive space.

I'm on the fence at the moment regarding achieving the capacity needed and ultimate reliability of a RAID 6 configuration but at the expense of not having a hot swap drive available for the OS RAID 1 array.  Yes, data integrity is certainly critical, but since I'll maintain daily differential and complete weekly backups I may just swing with RAID 5 leaving a universal hot swap drive available to either array.
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