First off, thank you very much for putting all this together. second, thank you very much for keeping it updated for over a year! I'm not sure how much time you've spent on forums, but it's likely you've noticed how rare that is.
I just purchased a MD3220, and I have a few questions about it that Dell won't (can't?) give me a straight answer on. I have a single MD3220 unit with 24 146GB 15K drives. Because our storage needs are very small (<1TB), it seems logical to me to simply raid a single RAID 10 disk group (plus cold spare) and divide that up in to 4 virtual disks. We only have about 20 VMs, with a varied workload (Exchange, Citrix XA and PVS, AD, file server w/ roaming profiles). However, you mention the following:
"don't split disk groups over multiple controllers if you can help it (one of the DAS tests below used that config and it was pitiful)"
I'm not exactly certain what you meant here, as disk groups don't have controller assignments? Rather, it's the virtual disks that are assigned. Are you saying that once a disk group is created, all its' associated virtual disks should be assigned to 1 controller? A Dell tech told me that they recommend a single virtual disk per disk group, but it seems like there's the potential for unnecessarily poor performance. Why give a disk group 6 disks when it coud have 24?
The only answer I can think of, would be that a sequential read/write might be interrupted by a random r/w on a different virtual disk (1 of many possible examples). From the MD3200 performance tuning guide:
"Dell™ does not recommend using more than four virtual disks or repositories per disk group for peak
performance. Additionally, where performance is critical, isolate virtual disks to separate disk groups
when possible. When multiple high traffic virtual disks share a disk group, even with purely sequential
usage models, the disk group I/O behavior becomes increasingly random, lowering overall performance."
I'm not specifically attached to the idea of having 4 virtual disks, that just seemed to be a good rule of thumb based on the above quote and http://www.yellow-bricks.com/2009/06/23/vmfslun-size/ (not the only sources I used, but the quickest explanation when accounting for total available capacity)
I've even considered short stroking a single RAID 6 disk group, as our few writes (<15%) are bursty but small in nature. Anybody have experience/thoughts on that vs a single RAID 10?
Finally, how many sectors did you give to iometer on these tests? I can't find any best practice info on sample size, only on read/write. For example, if my Exchange DB is 30GB, should I run a 30GB iometer test?
This is a brand new environment, so we'll most likely be doing ESXi 5. We only use the Essential Plus kit, so being an early adopter won't keep me up at night knowing that we're using the primary functions of ESXi that have been tested time and again for years - nothing bleeding edge.
