Raid Levels for virtualizing (Hyper-V)

Question

Hello,

In a PE2950III and perc 6ir with 8 HDD 146GB, which raid configuration can you suggest me for putting the vhd?

1* RAID 10 (8hdd)

2* RAID 10 (4hdd)

4* RAID 1 (2hdd)

2* RAID 1 (2hdd)(for OS) + 1* RAID 10(4hdd)(for DATA)

1* RAID 5 or 6 (8hdd)

The virtual servers will have databases, mailservers and webservers.

Thanks.

pcmeiners · Accepted Answer

'Enable write caching on the disk' ' Enable advanced performance (recommended only for disks with a backup power supply.'   The raid adapter takes controls of both disk cache/advanced performance, not the OS....  turned off as this interferes with raid safety/performance.   As to the other setting, the default values are generally best unless you have a specialized/dedicated server. You can play with WB, WT, read  and I/O policies with out doing damage.

pcmeiners · Accepted Answer

For a general use server the default is good, if you bench mark with the different read policies you will see minuscule differences. If you have a server dedicated to a specific program or to a specific task such as a group of users retrieving similar data, then the read policies may help. Daily defragging will give you 4-5% over an array which is defragged once a week or more.

pcmeiners · Accepted Answer

I do not see that much difference, except in the bust rate which means very little; your average speed and CPU usage are more important. You will always get variations (like in the IO test), but the read policy changes shows trade offs..what goes up or down in certain data size areas will be offset by changes in other data size areas; what do you think happens when the cache is filled with read ahead info.. something needs to be forced out of the cache. Secondly, most benchmarks highly stress arrays, flooding the cache..unless you have a couple hundred users hammering a server, your arrays will not blaze away or over stress the cache like benchmarks cause. If an array's disk LEDs are on as much as most benchmarks cause, it is time for an added server ( and a few extra cooling fans or "The Idiot's Guide to Cooking On a Hard Drive").

To get any meaningful benchmarks, you need to run multiple benchmarks, HD Tune/Tach and ATTO are not greats benchmarks, especially ATTO ( though good for cache speed comparisons). IOMeter, stop watch timed disk copies of averaged sized files within arrays (and over the network), SQLIO, and COSBI File Copy Benchmark, v0.52 are more realistic.

Check this out, for Win 2008, but unlike other previous MS tunning guides, it is accurate

http://www.microsoft.com/whdc/system/sysperf/Perf_tun_srv.mspx

Dev Mgr · Answer

How about a raid 1 for the OS (2 drives) and then a 6-disk raid 10 for the virtual machines.

The OS doesn't generate as much IO as the VMs combined and separating the boot disk from the 'data' disk is generally a good practice.

(post attempt 3)

festuc · Answer

Thanks for the reply.

It's similar to: 2* RAID 1 (2hdd)(for OS) + 1* RAID 10(4hdd)(for DATA)

I will try to made vhd's for OS's and put them in raid 1, and vhd for data and put them in raid 10.

Anybody knows what the next options values are suggested in virtual OS and using perc6ir?

1) Enable write caching on the disk

2) Enable advanced performance (recomended only for disks with a backup power supply.

On parent OS I cannot change this settings.

Finaly in server administrator, and are the values for the read policy and the write policy recomended?

Thanks a lot.

festuc · Answer

Thanks for the answer. I allready have deactivated them.

I have been playing with write cache in the perc controller and have advantages.

On the read side (adaptative read cache) I don't see improvement. Which setting do you recomend?

See: http://social.technet.microsoft.com/Forums/en-US/winserverhyperv/thread/5398a177-ff2f-498a-9a69-5c37d401a74b/

Thanks.

festuc · Answer

Thanks for the reply.

To tell the true I don't remember the defaults jajajaja anyway, if you look the before link the diference between no read cache and read cache towards read adaptative caché is very big.

Best Regards.

PowerEdge HDD/SCSI/RAID

Raid Levels for virtualizing (Hyper-V)

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