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SAN for SQL server

i will be purchasing a san for my sql server
want to create 3 RAID 10
one for tempdb 1 for log file 1 for data file
i need performance performance performance
my qiuestion is this the san will have 12 to 16 15k drives
to create 3 raid 10's i would only be able to give each raid 4 disks
if i create less raid 10's i can assign more disks to the raid 10
what would give me the best performance?
im interested in i/o writes not read
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Larry LarmeuPrincipal Consultant

Commented:
Pick a virtualized SAN, like an EqualLogic or HP EVA, and you can get more I/Os because you can run multiple RAID levels on the same disk set, giving you more spindles.
Larry LarmeuPrincipal Consultant

Commented:
If you use an HP EVA 4400, you can expect about 200 IOPS (i/o per second) per 15k disk.  With 1 full 12 disk enclosure, that is 2400 IOPS.  You can run all 3 RAID 10 LUNs on this 12 disk set, which will make them share IOPS on all 12 spindles, giving each one a maximum of 2400 IOPS, depending on the load of the other LUNs.  With a typical array, you would make 3 sets of 4 drives, and this would give you a maximum of 800 IOPS per LUN.  The great thing about the EVA, too, is that if you add more disks you can add more IOPS.  The SAN will spread the LUN over the newly added disks.  So if you were to later expand from 12 to 16 disks, you are adding 800 more IOPS to the mix.

Author

Commented:
the san will be either equalogic or EMC clarion

Author

Commented:
Pick a virtualized SAN, like an EqualLogic or HP EVA, and you can get more I/Os because you can run multiple RAID levels on the same disk set, giving you more spindles.

im not sure i understand this, are you saying that i can run multiple raids on same disks and get better performace then running raids on there own disks?
Larry LarmeuPrincipal Consultant

Commented:
I'm not that familiar with the Clariion, but with the EqualLogic you have to pick a RAID level per enclosure.  Pick RAID 10 and then you can create your 3 LUNs and they will share all 12-16 disks, giving you the most IOPS possible.  Breaking your array into smaller groups of disks decreases the maximum possible IOPS for the disk group.
Principal Consultant
Commented:
"im not sure i understand this, are you saying that i can run multiple raids on same disks and get better performace then running raids on there own disks?"


Yes - since most technology is not constantly running at 100% utilization, you can achieve better results by putting multiple LUNs on the same  disk group.  It raises your maximum possible IOPS.  In theory, if all of the LUNs were utilizing the hardware at the same rate, it would make no difference, but in actuality data is usually processed in bursts, so this will allow a busier LUN to have more resources available when one of the other LUNs is utilizing less of the hardware.

It's a similar concept to using VMware to virtualize multiple servers on 1 hardware platform.

Author

Commented:
so in my case where im bombarding the sql server with hundreds of transaction per second, would i achieve better performance on  multiple lun's on the same disk group vs raids with its own set of disks
Larry LarmeuPrincipal Consultant

Commented:
I would put them on the same disk group.  If the controllers are balancing the load properly, which they should, then the worst case scenario is that you would get equal performance to splitting the disks, but the best case scenario is that you will be able to get 3x the amount of IOPS.

Author

Commented:
is the emc clarion AX4 also a virtualized san, can i also create multiple volumes on the same disk group.
i read somewhere that the first 4 to 5 disks on the EMC clarion need to be on a raid 5 because it holds the OS.
if that is true i would only have 8 disks left for a raid 10.
also that would mean that you cant  pick a RAID level per enclosure as the equalogic
Larry LarmeuPrincipal Consultant

Commented:
I would highly recommend EQL over EMC if those are your two options.
Distinguished Expert 2019

Commented:
I would point out that MS best practices have the transaction logs on different spindles than the data, more for no loss restores than for performance.

Why are you buying a SAN though? you get more performance for the same price using direct attached storage. Are you clustering in future?

Author

Commented:
andyadler  i dont think i agree with you transaction logs in seperate raid gives you much better performance
also do not think you get better performance from  DAS over  SAN
Larry LarmeuPrincipal Consultant

Commented:
If the SAN is dedicated to the SQL server(s), the performance difference is fairly negligible, but if you are sharing the SAN with plenty of other applications the DAS would be faster.  DAS will not give you the flexibility that a SAN will, though.  It just depends on what your current needs are and what your future needs may be.

Author

Commented:
this san will be completely deticated to sql server

Author

Commented:
i guess my main decisiion at this point is to choose one over the other, the clarion is alot cheaper, but i dont think i can have the same type of raids where they share all disks in the array correct .
its not a virtualized SAN
Larry LarmeuPrincipal Consultant

Commented:
EMC is not virtualized, so you cannot add spindles to it.  You can put all of the RAIDs on one disk group, but the EMC does have extra overhead (their management system is the worst, IMO) and once you pick your disk group you are stuck with it.  So if you set up the disk group with 12 drives and later you think you need more spindles to increase the speed or capacity, you are stuck.  With the equal logic, you can add a second shelf and add those disks to the disk group to increase your IOPS.
Distinguished Expert 2019

Commented:
>andyadler  i dont think i agree with you transaction logs in seperate raid gives you much better performance

I didn't say that, I said the best practice is to have them seperat so that in the event of a failure of one set of spindles you can do a no losss restore since if you lose the log disks there's no loss and if you lose the data disks you restore and play back the logs.

>also do not think you get better performance from  DAS over  SAN

Again that's not what I said. I said you get more performance per the **same price**. Take a PS4000XV for example with 16 * 450GB 15K disks that'll cost you $39,000. Then look at how many RAID controllers, external enclosures and disks you can get for that price. All a SAN does for a single server is add an unneeded level of complexity and moves the disks further away from your CPU. Seperating the RAID controller from the server by adding a fibre channel or iSCSI connection adds latency, having powerful RAID controllers in the server is faster.

Commented:
Cost wise DAS is better , agree with andyalder, but for better perf SAN is best option.
It is always good to have log disks apart from data disks.Log disks are accessed more often and need faster B/W and less response time.
two Raid5(4+1) for data and one raid10(1+1) for logs =12 disks
 
There are many topologies you can carry with...
For feature use you can always add an additional enclosures... i did not find any wrong with EMC storage ...




Distinguished Expert 2019

Commented:
Better performance for same price? No way. I can afford twice as many spindles using DAS than you can afford using SAN so my DAS solution will be faster than your similarly priced SAN solution.

Commented:
I did not say same price... if the perf is considered SAN is recommended, obviously DAS is cheaper...
Distinguished Expert 2019

Commented:
And faster too because it hasn't got the additional latency of converting to serial, sending down fiber and then converting to parallel again. SAN can never beat DAS; you can put SSDs in your SAN box but I can put  LSISSS6200 or ioDrives inside the server in a DAS solution eliminating any fibre channel/SAS/Sata interface latency as the NAND flash is on the PCIe card itself.