HPVM advice sought

[John Kelly_3]

Hi, I'm soon going to install and maintain some VMs on an Integrity box with HDS SAN attached disks. I was considering placing my hosts either on raw LUNs or LVs. I would like to use LVs for the PVLinks but am wondering about the lesser performance. Does anyone have experience of both to comment on the difference? (Is the extra performance worth it if I then had to buy Secure Path to get multipathing?)
Each guest would have between 300G and 800G of disk space and there would be 8 guests on each host.

Another question I can't see an answer for is - does the VM support access to SAN attached tape drives?

[melvyn burnard]

I would suggest you take a read through some of the White Papers at:
http://docs.hp.com/en/vse.html#HP%20Integrity%20Virtual%20Machines

These may help you.
As for the SAN attached Tapes, no these are not currently supported

[Duncan Edmonstone · Accepted solution]

John,

From my perspective, if an app is sufficiently IO intensive to require load balancing across 2 modern (2 or 4Gb) HBAs, then it might not be a good candidate for a VM anyway. That said with the latest releases we do have AVIO which goes some way to speeding up IO in a VM so maybe... I wouldn't want to get tied down, but I would say if you expect to do a lot of sequential IO then go for disks rather than LVs. Presumably if you have a HDS disk array you'll need HDLM rather than Secure Path?

Does the VM support access to SAN tape drives - yes, but only 1 VM at a time. Basically you have to used the tape as an 'attached IO device' (see the manual), and add/remove the tape device to each VM as pre/post backup steps.

HTH

Duncan

[Duncan Edmonstone]

yikes! maybe I'm wrong on SAN attached tapes (I don't like to disagree with Melvyn!)

Will have to check some more

Duncan

[John Kelly_3]

I would attach multiple tape drives to one VM Guest and make it the Netbackup master and transfer data to be backed up over a private vswitch from the other guests.. Does that sound feasible?

[John Kelly_3]

Melvyn, see thread http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1195099 which talks about locally attached Tape drives. Are SAN attached drives a special case?

[Eric SAUBIGNAC]

Bonjour John,

You will find in "Best Practices for Integrity Virtual Machines" that raw LUNs have better performance than Logical volume. We can understand that, but ...

- from HP Hotliners at second level, it seems that performances with LVM as virtual storage is as good as raw devices and sometimes better. It was with HP VM 3.0 and of course it was not an HP's official advice ;-)

- I have moved some of my clients from raw devices as virtual storage to LVM as virtual storage without any degradation.

- Raw devices has several defects due to the fact that no hardware informations are transmitted to the guest : so you can't have mirror, nor pvlink inside the VM.

- I have experimented really bad things with autopath (correctly configured !) and raw devices as virtual storage : in a summary I had 2 active fabrics, decided to change FC cables one by one and waiting between each change for everything to return to normal state ... result was all VMs were frozed. Support told me they had that kind of problem on other sites, IMHO they had no good explanation the cause, but they clearly said that there is no problem like this with LVM ...

So I think I will definitively forget raw devices as virtual storage.

An other thing is to consider working with HP Integrity VM 3.5 : HP (in a non official way again ;-) agree that they have some difficulties with IO on version 3.0. If you take a look at CPU utilization inside the guest, you will probably see a high cpu utilization under %SYS (sar -u 5 100). This new version is said to have a great impact on that.

And no, San attached tape are not supported.

Regards Eric

[melvyn burnard]

Locally connected tape drives have been supported as "attached" devices since HP Integrity Virtual Machines version 2.0 (HP-UX guests only)
See page 13 of http://docs.hp.com/en/T2767-90033/T2767-90033.pdf

Version 3.0 extended this to other guests, see page 13 of http://docs.hp.com/en/T2767-90076/T2767-90076.pdf

But to my knowledge this is still only for locally attached devices, SAN attached tape support is a possible future. I will, however, check further to get thios confirmed or to correct a possible error on my part

[Eric SAUBIGNAC]

Well something else.

One advantage of configuring raw devices as virtual storage is that you can easly move from virtual to physical and from physical to virtual. With LVM in the host + LVM in the guest it is not possible.

This, plus trying to have the best performance with LVM as virtual storage, give me the idea to configure storage in the VM WITHOUT LVM for all of the virtual disks but vg00.

In other words, in the VM Guest I don't create FS over LV but directly on virtual raw devices. Advantages are :

- Better performance than having one LVM structure in the guest over one LVM structure in the host : I have just one LVM structure to cross in the host.
- Portability of all FS, but vg00, between physical and virtual environments. For vg00 I restore it from an ignite image.

Regards

Eric

[John Kelly_3]

Thanks/Merci to all for the interesting and informative responses. I will consider using LV due to the improved IO from AVIO on 3.5. I will also continue to read the White papers etc.

JohnK