Multipathed Fiber Channel disks as storage for VM Guests

[Maxim Yakimenko]

Dear collegues,
I want you to estimate my idea and propably give me some advises
I want to orginize storage for VM Guests with multipassing
My idea is that:
Suppose I have LUN on XP, this LUN is presented to VM Host and seen by server from 2 HBA, thus - 2 pathes. This LUN bases PV with 2 links. Then I create VG on it and in this VG I create LV and as storage device present to VM Guest.
One thing I don't like - LVM comes to scene in to places - ones at VM Host, and then on VM Guest, that sees LV as raw device an use it for creating its own VGS and placing partitions like /usr, /var and so.

May be there more convinent solution?

[Torsten.]

Hi,

the only other solution is to use a multipath product like secure/auto path.

(Of course you can use files as backing store also, but this would be slow).

See the manual about HP Integrity VM.

[Maxim Yakimenko]

This manual explains details poorly - I could not find any clue... :)

I used EVA for tests and securepath, with EVA securepath gets both pathes and presents to upper levels single device, that I used without help LVM on VM Hosts - is the same thing (single device file) true for XP? I heard that even I use SP I will have the same pathes, if so - what to do on Guest?

Also I have done some tests - I take 700MB file and download it from my PC to real server with storage based on LVM and localdisk and got speed 4-6Mb/s. Then I did the same for VM Guest, which storage was based on that securepath device - speed what 2,2 Mb - can it depend on something like size of pv or lv extent size?

[Torsten.]

refer to the install manual, chapter

6.2.1.3 VM Storage Multipath Solutions - page 66

[Maxim Yakimenko]

So I wonder how it will looks like if I want to present LUN from XP and use Autopath/Securepath for mulipathing?


And what is better:

1) Use PVLinks on VM Host, create VG and present LV from this VG to VM Guest.

2) Use Autopath/Securepath?

I heard that Securepath for XP is rather awkward and slow.

[noldi]

Hello Maxim,

the idea is to present a "Whole Disk" on the VM Host to the VM Guest and then do your Volume Management on the Guest only.

On the VM Guest you have only 1 path to the device through an SCSI HBA emulation layer, no matter how many paths it had on the VM Host.

In order to have Multipathing for "Whole disks" on the VM Host, you need an
unerlying driver that does this (SecurePath or AutoPath in our case). Using this extra software will be lifted with 11i v3 where Multipathing is built into the OS (using the Agile Storage Stack).

So, in fact probably the fastest storage stack would be Whole Disks both on the VM Host and the VM Guest (on the other hand maybe the least flexible . . .).

Best Regards,

Arnold

[Torsten.]

I set up some host as described in your plan A - using LVM (with pvlinks) on the host, present a LVOL to the guests. It works fine and fast.

Just make sure to use different HBAs of the host as the active path for the VG.

[Maxim Yakimenko]

Sorry to say I can not use tasty Agile View of 11v3 :)
And I want not only fast but reliable solution that can survive in case of, for exapmle,single FS switch failure - thats why I ask what is better - PVlinks on Host with presenting LV to Guest or Securepath on Host with presenting "raw device" to Guest - in first case we have LVM for creating multipathing with PVLinks on Host and LVM for storage managment on Guest; In second case - SecurePath for multipathing on Host and LVM for storage managment on Guest

[Maxim Yakimenko]

Ok, thanks, I just cant try this with XP

[Torsten.]

another idea: use striping to create striped LVOLs across different XP LUNs using both server HBAs for better performance.

[Maxim Yakimenko]

Well this is implied :)


Ok, thanx, guys, conclusion is clear

[Maxim Yakimenko]

Soon I'll try to test with XP