FAQ

On 6/10/11, Gordon Messmer wrote:
atime and mtime are updated for *every* read and write operation, not
for the open() of the file.
Ok. In any case, the combination of atime and ionice on the cronjob
seems to have helped, no locked up in the past 24 hours. But it is a
Saturday here so that might just be due to light usage, keeping
fingers crossed.
That aside, if you're running KVM I strongly recommend using LVM rather
than file-backed VM guests. It's more work to set up, but you'll see
drastically better IO performance in the guests. One system that I
measured had a write speed of around 8 MB/s for sequential block output
on file-backed VMs. LVM backed VMs wrote at around 56 MB/s for
sequential block output.

You should *never* used file-backed VMs for production systems.
The irony of it was that I decided to go with qcow2 because I thought
that would save overheads from an additional LVM layer but provided
snapshot capabilities too :(

Since I don't have enough spare space left on this particular system,
I'll probably have to get them to agree to add an extra disk to do the
LVM volumes, then figure out how to migrate the VM over from file to
raw/partition.

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