RAID 10 vs. 2x RAID 1 w/ 2 VMs

[Saugkraft]

Hi Community,

I'm switching from MS Hyper-V to VMWare 5.5.

At the moment I have 2 VMs in Hyper-V, each with a seperate RAID 1 (1 TB) on a LSI Onboard RAID Controller.

The Setup of the new machine is:

VMWare ESXi 5.5 U2, LSI 9240-8i RAID Controller, 4 identical HDDs.

Possible are 2 scenarios with this 4 1 TB HDDs.

- 2 datastores (2x RAID 1 w/ 1 TB each). Each VM has its own datastore with a separate 1 TB RAID 1 and a virtual disk in corresponding size.

- 1 datastore (1x RAID 10 w/ 2 TB). Each VM has its own virtual disk with 1 TB.

Both VMs are MS 2012 R2 Guests.

Which one should I prefer with regard of performance and reliability?

Thanks and best regards

Andre

[JarryG]

Concerning performance, the first thing you should do is to get different raid-controller. 9240-8i nas no cache and thus is unsuitable for ESXi (as we know, ESXi does *not* do disk-caching)...

But if we consider only "2x raid1 vs 1x raid10", then I'd recommend the second version. It allows you to get higher I/O if (at particular time) only single VM needs access to disks.

[Saugkraft]

Thanks Jarry,

I think in our scenario disk caching is not essential.

VM 1 is a IIS with a custom website based on ASP (we have a second dedicated MS-SQL host for DB access). There are about 500-800 users at  peak times.

VM 2 is a Adobe Connect Server (also accessing the dedicated MS-SQL host) with a maximum of ~250 concurrent users.

The hole solution is just a SBS. Therefore I think that no-caching is not the problem. Actually we don't have disk performance problems. That's not the point.

This server is a new one and the first with VMWare. So I'd like to get some advices like "makes no difference", "dont't do ... with VMWare", "if you setup your host like .. you'll possibly get into trouble because ..".

The setup w/ 2x RAID 1 ist historical and vor MS Hyper-V a good solution. If VMWare (I'm a newbie) can handle 1 RAID 10 better, I'd use my brain for thinking about other ways of setting up my servers.

[JarryG]

"...Actually we don't have disk performance problems..."

Trust me, you are about to have them if you move your VMs to ESXi with raid-controller without cache. Hyper-V does disk-caching, but ESXi does *not*. And that makes huge difference. Without caching (and depending on disk defragmentation) your effective random R/W speed with classical spin-drives may drop deep below 1MB/s (and that's for single VM, and single queue). Just search a little this forum for datastore-performance complains. You'll find plenty of them.

OK, it's your decision, but I have warned you. BTW, just out of curiosity: If R/W-speed is not important for you, then why do you bother with "2x raid1 or 1x raid10" dilema? Because "with or without disk-caching" makes much more difference, than "raid1 or raid0 or raid10"...

[Saugkraft]

Thanks.

My question was: Which configuration is the better one?

1. 1x RAID 10 with 2 virtual disks on one dataspace.

or

2. 2x RAID 1 with 2 hardwarew separated virtual Disks.

Trust me. Actually I have a LSI Software "Fake RAID" with a 3 GB Controller. That fits. The performance is sufficient.

Sufficient. That means sufficient. No problems.

3 GB Software "Fake RAID".

My question: please read the first post.

My secondary question was: Which controller shoul I use instead? You didn't answer that.

Did you get that?

Thanks again.

This is no "I feel like.."-event.

Clear question, clear answer. If you can (without feelings).

Thanks again. (Third time)

[JarryG]

I already answered your question (check my first post: raid10 with two VMs on the same datastore can be slightly better than 2x raid1 with vdisk on separate arrays. But I really do not know how efficiently raid-controller can handle this without cache. Never used non-cached drives for serious application...

And concerning your second one: well, any with on-board cache (the faster&bigger the better) and power-backup (battery or capacitor). There are many of them. If you prefer LSI, then anything above 9260 (and oem-models)...

[Saugkraft]

That sounds conclusive. Thank you.

JarryG schrieb:

OK, it's your decision, but I have warned you. BTW, just out of curiosity: If R/W-speed is not important for you, then why do you bother with "2x raid1 or 1x raid10" dilema? Because "with or without disk-caching" makes much more difference, than "raid1 or raid0 or raid10"...

I don't really bother with this question if it makes no real difference. I just wanted to exclude potential problems like "..you shouldn't host two VMs on one datastore because.."

Perhaps there are/could have been other details I should consider. "Backup is easier if..", "If you use different datastores you can.." Things like that.

The devil is in the detail and I'm new to VMWare. From this point of view you'll never know if you don't ask.

Anyway.. I'll think about your arguments. It seems that I should do the job properly: upgrade to a controller w/ cache and BBU/Flash and setup RAID 10 with a hotspare. When if not now.

I don't really prefer LSI. The 9240 is from a prior XenServer for testing different OSes (with the cheaper Adaptec controllers there are some compatibility issues on Xen)

For the new one Adaptec should also do the trick. What about the 7805?

[JarryG]

Adaptec 7805 is a good controller, but iirc cache-protection is optional, and has to be purchased separately. Basically you do not need it if you have good UPS, but some controllers do not allow to use cache for write-ops when no battery is detected. I'm not sure how it is with Adaptec...

And one more thing: I recommend to check compatibility with ESXi very carefully. Do not rely purely on VMware hardware-compatibility list. I had some Adaptec-controller in the past (some of "5" or "6" series, don't remember exact type), according to VMware it was "supported". Yes, it was. There was driver for it included in install-image, raid-arrays were detected, and I could use it for ESXi. But there was no smis-provider for it (confirmed later by Adaptec), and thus no way to monitor its health. What is such a raid-controller good for?

[Saugkraft]

After some research, I guess that LSI provides a better compatibility than Adaptec. Adaptec provides drivers for VMWare but I didn't found some hints for native support without installing drivers (this corresponds with my experiences with XenServer).

Which controllers do you prefer? LSI, Adaptec? Any hint would help me for further investigations.

[JarryG]

I personally now use reseller-versions of LSI controllers (IBM-Mxxx, Intel-RS/RM/RT, Fujitsu Dxxx, Dell Perc, etc). They are usually cheaper and sometime come better equipped. Right now I'm running two ESXi-servers with IBM M5016, which is basically oem-version of LSI-9266, but it comes already with super-capacitor (lasts longer than battery) and raid6-support. I got them new for ~250€ each on eBay. And the good thing is, one can use original LSI-bios, tools, firmware and drivers. You can find list of original and oem-models with basic description and differencies here:

LSI RAID Controller and HBA Complete Listing Plus OEM Models | ServeTheHome and ServeThe.Biz Forums

[Saugkraft]

Ok. Thank you. I think I'll use the 9271-8i. (Worth a try)

Actual problem (that's what I meant when I said: be aware..):

I had a single drive (JBOD) on the onboard controller. Attached to the VM. Now I removed the physical HDD -> the VM didn't start. That's my worst case. The VM must/should star in case of a hardware failure/misconfiguration.

Which means (for me - and that's the answer I did expect and which I learnt by accident): Let the controller do the job.

I don't know how experienced you are with Hyper-V. THIS case would not prevent the VM from starting (by default). There would be just one backupp HDD missing. And this are these "devil is in the detail"-things I'd like to eleminate (I'm still new to VMWare :smileygrin:).

Conclusion: Reliable Controller with VMWare support, RAID 10, Hotspare, etc. I still think in physical volumes. I should reconsider this. It seems, that one datestore with different virtual volumes is the better way in VMWare. If you use Hyper-V it's the opposite.

Thank you very much. This discussion is very helpful.