Help with LUN/RAID Array

Bob,

do you already have 600Gb drive hot spare ?

Yes, we actually purchased a total of 16 disk, 15 in the new DAE, and then one to go into another Fibre Channel DAE enclosure that has room. When I spec'ed this out to my management, I explained that we’d lose one drive for the hot spare and one for RAID 5 Parity, but that was before I knew I couldn’t do one large LUN. So I’m trying to not eat up to many of these 600Gb drives…

so even if you did 14+1 R5 configuration, that would give you 7.5 terabytes usable. EMC best practice for raid-5 is either 4+1 or 8+1 but nothing will stop you from creating a much larger raid group (max 16 drives). Do you need all that capacity available at once ?

No, not necessarily. But it depends on how I can break up that total space. For example, if I create the 14+1 R5 giving me the 7.5 TBs, which would be great, do I then create multiple LUNs from within that space and allocate to what ever server/host I need to?

I have to divide up the space between the two projects. I need at least 3TBs for VMware, but I don't need an additional 4TB for expanding the current servers, I could probably get away with just 2TB for expansions. However I need to keep in mind for future growth on both sides.

The LUNs for the VMware has to be broken up into smaller LUNS, something like 2 500GB LUNs per host, I have 3 host. Then I need to expand the other servers I have as well, two SQL servers that utilize the SAN for storage. I'd prefer to simply expand on those SQL server partition they currently use vs giving them new ones.

My concern with creating the 14 R5 is that I have to make sure that doesn't add to or cause any SCSI reservation in the VM side or any other VM side effects I haven't read up on yet.

Now I could probably get away with doing an 8 drive R5, approx 4.2 TB useable, on one and then doing a 7 drive R5, approx 3.6TB useable for the other. But again do I break up that storage to create multiple LUNs?

Also I'm assuming when you do the +1 that is my hotswap, right? Can the hotswap drive apply to both RAID groups?

Thanks!

Bob

yes, you create a raid group and start creating LUNs from it. You have to consider the negative things about having large raid groups like that: higher probability of double drive failure ..more drives in the raid group, higher probability.  Large raid groups take longer rebuild so there is a longer impact while drive is being rebuild to hot spare. It also sounds like you are designing for capacity but what about performance. Do you have any performance requirements ?

Take a look at this excellent guide for more ideas

White Paper: EMC CLARiiON Best Practices for Fibre Channel Storage: FLARE Release 26 Firmware Update - Best Practices Planning

Yes, performance is probably a bigger factor than capacity, especially since we’re working with both virtualization (VMware) and SQL, (not in combo, separate projects) but I need to do my best to keep capacity up near the top of the list. My management isn't looking to purchase any more storage for some time, mostly based on the premises of what I "thought" we needed and purchased already. I really don't want to have to go back to them with my hand out asking for more. I need to make this as balanced as possible between performance, capacity, and scalability with what I have.

I will check out the PDF.

Thanks for your help!

Bob