How will Flare handle lun in a thin pool , when expanding with more disks

John,

What version of Flare are you running in this scenario, Thin pools have been around since flare 28xxxxx.  Below flare 30 there is no auto load balancing of a LUN within a Thin Pool.  When you create the LUN in a Thin Pool its thinly allocated so you provision a 100gb LUN but the pool allocates just 1gb LUN initally.  Since your using 20 disks in a raid 5 Thin Pool(TP), the TP has created in the background 4+1 for every 5 of your 20 disks.  So first 1 gb slice is from the first 4+1 in the pool   As your LUN begins to use space the pool allocates the next 1gb slice from the next 4+1 and so on and so on where it eventually wraps back around.  Your LUN is now a bunch of slices from the pool but presented as a single LUN.  So if you were to add disks later on to the pool and you wanted to relevel and you had the space, LUN migration within the same pool would be needed.

IN flare 30, be sure to get Fast 2 because it auto levels these individual 1gb slices.  Your LUN can now live on EFD, FC and SATA based on needed performance.  So releveling is not so much concern any more.  Definately read up on Thin Pool allocation and Fast 2 becuase there is huge benefits there.

Thanks,

Mike

Mike, your reply was a little vague. You say that we should read up on FAST 2, which is fine; however, are you saying that with R30, and FAST 2, you get auto-leveling within the same drive type, but not without FAST 2?

For example, if I have R30, and I have 20 FC drives in a pool, then I add 5 more drives, walk me through where the data goes. If I add 100GB of data, which spindles does that 100GB go to? And, what happens to the 2TB of data that was on the original 20 drives?

I would like to see more transparency about Storage Pools from EMC. More white papers, more scenario based discussions, etc. Those of us that have lived in the real (non virtual, non thin) world for many years are hesitant to throw out all our best practices and rely on the array to figure it out for us. We need to know more details about where our data is so that we can prevent hotspots and better tune our environment. Before I start throwing SATA drives in an FC pool, I'm going to want to feel comfortable expanding FC with FC - which I hope does not require FAST to get full benefits. I read in one of EMC's detailed reviews that it is "recommended" to expand thin pools with the same number of disks you start out with. To me, this is sounds like MetaLUNs - striped vs concatenation - and needs more explanation.

Thank you,

Jason Burroughs

I did some testing on storage pools. Here are my findings: http://virtualeverything.wordpress.com/2011/03/05/emc-storage-pool-deep-dive-design-considerations-caveats/

Appreciate any feedback/corrections/etc.

Thanks.

/vijay