choosing RAID policy

Hello Huw,

 Nice thing about Dell PS series storage is later you can go from R10 to R50/6 w/o losing data.  It will expand to a greater capacity RAID level.  You just can't do the reverse.

Exchange, and VMware tend to be smaller size IO, but with greater randomness.  Which is best served by R10.  What is "RDS"?

The warning about using R6 w/7.2K drives is they take much longer to rebuild, because they are slower, and getting larger and larger these days.  10K/15K drives are so much faster and smaller their rebuild times are much better.   Also the rebuild time is also dependent on load.   More load equals longer rebuilds.

I would suggest starting with R10.  Install SANHQ and monitor the I/O pattern.   Also use thin provisioned volumes on the EQL side.  VMware VMFS, Windows 2K8+ (w/HIT/KIT)  Windows 2K12+ all support UNMAP.   Also known as space reclaim.   With VMFS that's a manual process at the VMware CLI.  

For Windows, if you use the MS iSCSI initiator to connect to the volume, (even on a VM in VMware) you can install the HIT/ME software.  Available on the EQLSUPPORT.DELL.COM website.  This provides enhanced MPIO, integration with SQL, Exchange and SharePoint.   Providing consistent snapshots and adding UNMAP support to Windows 2K8.  Again it's native in W2K12+

RAID50 vs. R6.  Once you get some data in SANHQ there's a RAID evaluator. You can preview different RAID levels using the existing data.  Gives you an idea on the possible performance impact.

R50 is slightly faster than R6, however the 4210 is the current gen controller and it pretty fast. Combined with 10K drives rebuild times shouldn't really be much different.  The software also has detection for impending failures. If triggered it will mirror the failing drive out first, instead of forcing a rebuild.  

The only con against R50, is that it's two R5 RAIDsets striped together.  So if there's a failure during a rebuild the RAIDset fails, and all volumes go offline.   R6 is the safest RAID level by far, but comes at a performance cost on writes.  However READs are better on R50/R6 compared to R10.

There's a tech report that has more info on choosing RAID policy.

It's available here:

en.community.dell.com/.../new-equallogic-raid-tech-report-considerations-and-best-practices-released

There is a best practice guide for VMware + EQL storage.  It's very important to set it up correctly the first time.  Fixing it afterwards requires much more time as it requires maint mode and reboot.

It's available here:

en.community.dell.com/.../20434601

Something that gets missed is when formatting your NTFS volumes (or VMDKs),  do accept the default allocation size.  It says "auto".  Change that to 64K.  You can't do that on C: drives, but all data drives should be formatted that way.  This aligns I/O on the 64K stripe used on the Dell PS Series SAN.  Especially when running R50/R6 this can improve the efficiency of all writes.  It's known as a "full stripe write" in RAID terms.  It takes the least amount of operations to do such a write.  Partial stripe writes require more operations.  Works fine for R10 as well.  

Hope this helps.

Regards,

Don