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On Mar 16, 2012, at 12:26, "Pádraig Brady" <p...@draigbrady.com> wrote: > On 03/16/2012 04:11 PM, Jay Pipes wrote: >> Hi Stackers, >> >> So, in diagnosing a few things on TryStack yesterday, I ran into an >> interesting problem with snapshotting that I'm hoping to get some advice on. >> >> == The Problem == >> > >> QEMU was unhelpfully returning a vague error message of "error while >> writing". > > That could be improved. > As an aside, since qemu-img is mainly dealing with large files, > it would be a prime candidate to call fallocate() from > to get good layout for the files and immediate feedback > if there isn't enough space. > > On a related note, I've a patch pending for after RC1 > that should auto clean any of these partially written files: > https://review.openstack.org/#change,5442 > >> As it turns out, the base operating system we install on our compute nodes >> in TryStack has a (very) small root partition > >> == Possible Solutions == >> >> So, there are a number of solutions that we can work on here, and I'm >> wondering what the preference would be. Here are the solutions I have come >> up with, along with a no-brainer improvement to Nova that would help in >> diagnosing this problem: >> >> The no-brainer: Detect before attempting a snapshot that there is enough >> space on a device to perform the operation, and if not, throw a useful error >> message up the stack > > The space can change while writing, so you could still get the same error > above. > >> >> Solutions to the disk space problem: >> >> (1) Silly Jay, change the damn size of the root partition in your PXE base >> OS install! >> >> Now, I'm no expert in creating customized base disk images, but from looking >> at the build_pxe_env.sh script in devstack [1], it seems pretty trivial to >> change the ramdisk_size parameter in the startup options to something larger >> than 2109600. We could do this and reimage the compute nodes one by one. >> >> (2) Make the location in which the snapshot is made configurable. >> >> Right now, as mentioned above, tempfile.mkdtemp() is used, which creates a >> directory in the user's TMPDIR (typically /tmp, which is usually on the root >> partition). >> >> We could add an option (--libvirt-snapshot-dir?) that would allow >> nova-compute to override where that snapshot is built. >> >> (3) Change the user (running nova-compute) TMPDIR setting to something >> different than /tmp on the root partition). > > I'd lean towards (3). > That's something that depends on the environment (as you've nicely > demonstrated), > and also for security reasons the admin should be able to set TMPDIR. > That's the standard way to do it, and it works already (hopefully). Actually I would argue that the best way to accomplish this would be option #2. That way an admin/operator has control over the location. Not manipulating this by messing around with a users environment variable. > > cheers, > Pádraig. > > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : openstack@lists.launchpad.net > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
