Re: DC RAID Configuration

I have not seen MSFT produce a definitive guide because every individual situation and environment differ. With many architectural decisions, there are many ways you could go. For my small business customers, we often use six disks on a built-in RAID controller (both SCSI and SATA). First two disks are mirrored and the last four are RAID5 with one hot swap. Then we also backup to tape or online backup provider so that we're not relying on either RAID array to be the only form of backup.

I have heard about how MSFT does their own internal DC's and I have never seen such redundant redundancy in a server spec before or since. I don't remember all the specifics, but they did something like a mirrored stripe set with four disks for the OS, then a mirrored stripe with parity for the second volume with six more disks on a separate controller. Something along those lines. I'd never seen so many disks used in a single server that wasn't hosting huge amounts of data.

If I'm guessing right about the load you'll have on these servers (if they're only DC's and not running other major server apps), with 30 DC's servicing 2500 users distributed across the system geographically, you're averaging between 50 and 100 users per DC. With a load like that, you have a lot of flexibility in your configuration. If you were serving 2500 users on a single pair of DC's, it would be much more important where you put the dit file and the pagefile.

The one thing I would require on a server I was building is the battery backup on the RAID card. It doesn't make a lot of sense to me to spend the kind of money you're talking about, with good redundancy and then end up dropping data off the RAID controller.

In this scenario, I would be tempted to create two stripe sets (with or without parity depending on the performance I needed) and mirror them. I have read a lot of arguments against using RAID5, but in my personal experience, 10 years spanning life as a sysadmin, support engineer at msft and a small business IT consultant, I've never seen two disks in one RAID5 fail at the same time (I hope I didn't just tempt fate).

When I worked at msft I occasionally reviewed AD architecture plans for large consulting organizations. I (and my teammates) would give approval on any setup that provided adequate redundancy and I never saw any specific configuration that was used more than another. It was always dependent on the overall scenario more than anything else.

If my assumptions about the load on these DC's are right, I would mirror two 3 disk RAID5 sets on each DC. That's certainly not the most high performance configuration for that hardware, but it also makes it very unlikely that you'll suffer a failure of one of those servers because of disk issues. Higher performance would be to mirror a stripe set (RAID0, no parity), you'd get the redundancy of the mirroring, but faster reads and writes.

If you want to provide more specifics about the environment and expected load on these DC's, that might make it easier to narrow down the scope of options you have.

Hope this feedback helps you decide which way is right for your environment.

Happy Thanksgiving!

--
Mike Shepperd
Sunfire Solutions LLC
Seattle, WA

[This posting is provided AS-IS, with no warranties and confers no rights]


"jamestulloch" <james@xxxxxxxxxxxxxxxx> wrote in message news:1164278888.971223.323740@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi,

I have to deploy about 30 2003 DCs. 2500 users across 40 Europe wide
locations. Each server has 6 disks. I have two issues.

1) Do I make three mirrors and put OS on 1, SYSVOL on 2 and NTDS.dit
on 3. Ten where does the page file go? I have 2GB memory.

2) My onboard RAID Controller does not have battery back up. Do I
insiste that we get new cards or should we stick with onboard. If we do
should I enable write back on the cache.

Any thoughts? Joe from Joeware published a response to a similar
question in 2004, but nowhere I look does MS say. HP recommend the
above but dont mention page file. I am proposing keeing it with the OS
unless soemone out there can give me a more definite pointer.

TIA

James


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