Combining SAS/SATA disks with Tiered Storage??

[Tom Lyczko]

Is anyone doing this??
SSDs are still too expensive for us.

We will not have a huge quantity of users for a 2-node cluster in the foreseeable future...initially 35-50 growing to maybe 100-some.

We will have several databases and an email server.

I am thinking of several 15k 600 GB SAS drives as Tier 0 and several MDL/nearline SATA drives.

Comments/suggestions appreciated.

Thank you, Tom

[oikjn]

I"m doing SSD+7.2kSATA, but really it doesn't matter, faster/slower, how much of either there it will work the same either way. One thing to think about though is that it seems to want to heavily favor Tier0 over Tier1 as long as there is storage capacity, so it will fill Tier0 and then move to Tier1 only after tier0 is full or it will go strait to Tier1 if the LUN isn't AO enabled. It does move data around to make sure Tier0 is filled with "hot" data over "cold" data, but if your data set happens to be smaller than the size of tier0, then 100% of it will go there. I bring that up because if you have two tiers of storage that are really close in performance, it might not pay to split them into tiers if that will cause most of the IO to go into one set over the other, but that would be up to you.

[a_o]

Are your StoreVirtual units SATA only?

IMO, when running StoreVirtual, SATA should really only come into play if you're using your LUNs for long term archival purposes. Those drives tend to be bigger and slower in any case., and have the attendant problems with long RAID rebuild times.

In my cursory testing, there was not enough of a performance boost in using SAS/SATA in Tier0/Tier1, vs SATA only for this specific (archival)  kind of use.  But the performance was also affected by the amount of data being moved/stored during each backup that we were running. (i.e. >3TB) .  The test had two 450GB 15K (R1) drives as Tier0.
So it was inefficient from a performance  and a storage yield POV . i.e  450GB (SAS) vs. 6TB (SATA) for the two 3.5" disks being used.

With  SSD/(SAS/SATA), the write performance gets boosted because in Tier0, as the physical RAID is usually R0 or R1 vs R5 for the Tier 1 (SAS/SATA).

If you're running SQLdatabase  on your setup, depending on your LUN sizes, even the addition of a single SSD drive to each StoreVirtual unit will make a noticeable difference.

[David_Tocker]

I dont think AO was ever intended to be used in a use case such as 2x 15k sas with 6x 7.2k sata.

The fact is the IOPS between the two media are going to be so poor as to kill the benefits of moving the hot data to the faster media (using -more- iops) A valid use case for AO might be 8x 200GB SSD in pool 0 and 24x 600gb SAS in pool 1. 
(or something along those lines)

[Tom Lyczko]

Thanks David...

Your suggestion is good if I had $3,449,344.84 to spend. :)

Wonder if it would be worthwhile with one SSD say 500 GB and 11 x 600 SAS???

Looks like I will go with 8-9 SAS and leave 3-4 bays empty, then add more disks later on...

Thank you, Tom

[oikjn]

I wouldn't go to the extreeme that David said there, but YMMV.  It doesn't appear to move data around between tiers a ton from what I can tell.  The key is that you have to consider throughput, I/O capacity, and I/O latency, if your tier-0 isn't clearly suverior in all three of those categories, your benefit for having a two-tier system will be limited.  I've done raid-5 set of 5 512GB SSDs and a raid-5 set of 5 2TB SATA disks for a two-node cluster (each raid set was done in hardware and presented each as a disk to the VSA) and have been pretty happy with the performance using it generally as general VM storage.

[David_Tocker]

Bang on. (Yeah my config might have been a little over the top :) )

Still - everything should be raid (including your SSD) so perhaps a better use case would be 2x 200GB SSD, 8x 2GB 7.2K.

At the end of the day it really depends on you environment and what you can afford... I would rather a single node P4000 with everything raided than two nodes with the underlying storage unprotected...

[oikjn]

for whatever its worth, I've tried desktop SSDs like the crucial M500 in raid10 and raid5 and they are great for intermittent loads, but a long-term sustained load really requires an enterprise level SSD.  In my case, I'm able to get away with a raid5 group of 5 M500's on two nodes which gave me ~1.9TB usable space as a Tier0 area on a two-node cluster for under $2500.