Posted on 2013-01-16
Last Modified: 2016-11-23

Happy New Year to you.  Looking for a SAN that would work well with Dell Servers in an vmware environment.

Dell SANS apparently do support 15K SAS disks, with a trade off of available disk space.  We were looking at a Dell SAN and the biggest disk we could get was 300 GB @ 15K, which wouldn't give us the storage we need.

600 GB disks are 10K SAS.

Thanks for the help in advance
Question by:cmatchett
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LVL 122

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 167 total points
ID: 38784003
Dell Equallogic PS4100

How much storage do you want, we have approx 14TB (raw), 24 x 600 disks!
LVL 37

Assisted Solution

by:Neil Russell
Neil Russell earned 167 total points
ID: 38784011
Using an Equallogic SAN with 10K SAS disks will give you NO problems with vmware at all.

You can of course go to the PS series and tiered storage, if your budget fits. It is NOT always JUST about disk spin speeds.
LVL 37

Expert Comment

by:Neil Russell
ID: 38784035
All on Dell Equallogic Storage.
All of the above is on Equallogic tiered storage.
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Author Comment

ID: 38784083
Sorry, I should have put on the first post that this company run a database and the company who develop it, say they will only support it when it is running15k disks.  We have our dell san with 600 gb disks (12tb) with a RAID 10.  These are 10k

Dell only do disks with 15k @ 300 GB.  That would reduce our storage by 50%.

we have thought about getting a second chasis with 300gb disks dedicated for SQL...
LVL 122
ID: 38784161
how many IOPS does your database require?

ask your developers this question.

Author Comment

ID: 38784239
Hey Hancock, they said under no circumstances would they ever support the database on anything less than 15k disks.  Period.

I suppose they are just protecting themselves that way.  

Do you reckon that you could still get the required performance on 10k disks? if they met the IOP requirements?
LVL 122
ID: 38784349
databases are all about IOPS not the technology underneath, virtualising the database reduces the IOPS because the I/O is virtualised.

increasing the disks in the stripe, will increase the IOPS.
LVL 37

Expert Comment

by:Neil Russell
ID: 38784368
Sounds verymuch like your supplier knows very little about virtualization!

As hanccocka said and I said earlier, its not about spin speed, its all about IOPS.

Author Comment

ID: 38784488
I will come back with this information. thanks
LVL 122
ID: 38784533
We have weekly meetings with Clients and their Vendors, because they state, we will only support the software, database, application, if it's Dell, HP, IBM, has this technology or that technology.

and what we find, is that because they have only ever tested their tiny little application, on their test bed, they will not deviate from their baseline.

we even had one vendor this week, through the same argument, that their application needed 15k disks only.

When we gave them a solution to trial, that would give their application, at ~200,000 IOPS and >800MB/s, they told us it was slow!

We asked them to try the same tests on their test bed at their offices, and they could only yield 603 IOPS!

and if you are wondering what yeilds so high IOPS, SSDs, is your vendor going to say no to SSDs, because they want 15k rotational old hard drives!?
LVL 37

Expert Comment

by:Neil Russell
ID: 38784584
We have the PS6100XVS  with a mix of SAS and SSD disks and under testing we got a consistant 45000 IOPS under load.

Author Comment

ID: 38784758
Is there a IOP calculator that use would recommend when i have the information
LVL 122
ID: 38784774
Some very rough quick calculations

Total IOPS = (DriveIOPS * #Drives) / (ReadRatio + (RAIDWritePenalty * WriteRatio))

RAID 10 6 x 7,200 RPM SATA drive - Approx 50 IOPS each disk. assuming 33% Writes

Total IOPS = (50 IOPS x 6 disks)/(.67 + 2*.33))
           = 225 IOPS

RAID 5 6 x 600 SAS 15k Drives - Approx 200 IOPS each disk. assuming 33% writes

Total IOPS = (200 IOPS x 6 disks)/(0.67+4*.33))
           = 603 IOPS

Difference = 378 IOPS

We already know some numbers about IOPS per disk (assuming a reasonable latency and random access)


SAS (15K RPM)        - 175 IOPS

SATA (7.2K RPM)     -  75  IOPS


But how to double check if these numbers are ok or not?



IOPS Estimated = 1 / ((seek time / 1000) + (latency / 1000)

Let's make a simple test:

 SAS - 600GB 15K - Seagate -

 Estimated IOPS = 1 / ( ( (average read seek time+average write seek time) / 2) / 1000) + (average latency / 1000)

 Estimated IOPS = 1 / ((3.65 / 1000) + (2.0 / 1000) = 1 / (0.00365) + (0.002) = 176.99115044247787610619469026549 - ~ 175 IOPS

 SATA - 1TB 7.2K - Seagate -

 Estimated IOPS = 1 / ( ( (average read seek time+average write seek time) / 2) / 1000) + (average latency / 1000)

 Estimated IOPS = 1 / ((9.00 / 1000) + (4.16 / 1000) = 1 / (0.009) + (0.00416) = 75.987841945288753799392097264438 - ~ 75 IOPS

 Based on the calculation, those numbers above are OK
LVL 10

Assisted Solution

millardjk earned 166 total points
ID: 38786972
To stay in your Dell-only environment, you could also look into using NexentaStor on Dell-branded gear. See for some example architecture; you can substitute 15k drives if the vendor is going to be absolutist about the solution, adding additional drive trays to get to your desired capacity.

However, the other Experts that have pointed out that its all about IOPS (and thruput) are right; that's why Dell offers the PS4500 series in the first place: pair 2 SATA drives (in a proper array) get the same performance as a single 10K disk. You pay for more in space/power/cooling to go SATA, but you can also get higher capacity per-disk: 2x2TB (raw) vs 600GB. A PS4500 with 2TB drives yields 96TB raw capacity (before establishing RAID levels) and will pool-up under RAID10 for 46TB--and the performance is equivalent to the PS4100XV, all in 3U of space instead of 2U.

Author Comment

ID: 38816582
still waiting on answer for this

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