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Re: [Xen-API] XCP 1.1 Intellicache issues

Hi Lars,

Intellicache certainly won't work when VMPP is doing stuff.

Getting intellicache to work is slightly tricky - it assumes a VHD chain length 
of exactly two. VMPP will cause the chain length to increase and thus violate 
that assumption. I'd be surprised if doing that actually causes corruption, but 
I've been surprised before, and no doubt I'll be surprised again at some point 
in the future :-)

So, I think my advice at the moment is to turn off VMPP and try again to see 
whether you still see the issues.


On 14 Oct 2011, at 10:01, Lars Seeliger wrote:

> Hi there,
> We've just upgraded to XCP 1.1, and I'm testing Intellicache to see what 
> performance benefits it could possibly bring to our infrastructure. I'm 
> running a Windows 7 VM from an NFS SR, the local storage on the XCP host has 
> caching enabled. So far, so good.
> I ran the following command:
> xe vdi-param-set uuid=75eaac3e-d2ec-4f45-ac9f-67586f2d703c allow-caching=true 
> on-boot=persist
> which enabled caching on the c: of the VM in question. Using dstat on the XCP 
> host, I can see now how when a programme is used data is written to the local 
> SR and pulled from there on next launch. Although the local storage isn't the 
> fastest (I'll be installing an SSD soon), Intellicache clearly makes a 
> difference, as we have a few VMs competing for I/O on that NFS SR. Anyway, I 
> have noticed a couple of oddities; I rebooted the VM now to test boot speed 
> and Windows forced a chkdsk. Many errors are being found. Before the reboot, 
> I noticed my Firefox profile was somehow missing/outdated. Using Previous 
> Versions I managed to restore a working copy.
> Once Wiindows is back up and running, I'll bet my outlook .ost file is 
> corrupt. This is exactly the same behaviour I noticed with the unsupported 
> Intellicache in XCP 1.0. I assumed when I tested it back then that the 
> technology was in a testing phase and these sorts of issues would be sorted 
> by the time 1.1 was released. So either there is a problem or I'm doing 
> something wrong (I hope the latter!)
> I have a feeling this is related to snapshots; the VM is a member of a VM 
> Protection Policy, which performs a simple disk snapshot nightly at 23:00. 
> But who knows?
> So, any clues? I'd appreciate any help working out what's causing this 
> corruption.
> Thanks.
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