On Mon, 15 Oct 2012, Daniel Pittman <daniel@rimspace.net> wrote:
For the mail spool a zvol would be a bad idea, fsck on a 400G Ext3/4 filesystem is a bad thing and having the double filesystem overhead of Ext3/4 on top of a zvol is going to suck for the most disk intensive filesystem.
zvol is more like an LVM logical volume than a filesystem, so the overhead isn't nearly as much as this comment suggests. That said, running ext3 (especially) or ext4 on top of it is going to be slower, and means you can't use the RAID style features of ZFS, and you give up object level checksums.
I had the impression that a zvol gets all the consistency benefits of ZFS but for a block device. ZFS on top of a zvol may not be a good idea as ZFS is fairly heavy, BTRFS on top of a zvol might be an option though.
Any suggestions?
I would aim to run ZFS in the mail domU, and treat the zvol as a "logical volume" block device. You will have some overhead from the double checksums, but robust performance. It treats the underlying dom0 ZFS as a fancy LVM, essentially. You probably also need to allocate substantially more memory to the domU than you would otherwise.
Yes, lots more RAM in both Dom0 and DomU. The problem is that I have servers with 16G of RAM that I'd prefer not to upgrade.
My fallback would be NFS shared ZFS in the domU - much cheaper because you only have one ARC, set of checksums, etc, to manage, but with the added bonus of NFS between the domU and dom0. Fun times.
Are you sure that LXC or OpenVZ wouldn't better fit your needs than Xen? You trade off marginally less isolation between containers for the simplicity of having a single kernel image - so native ZFS performance.
That's a possibility. What is the support for them like in Debian/Wheezy? On Mon, 15 Oct 2012, Jason White <jason@jasonjgw.net> wrote:
XFS doesn't have the fsck problem, but it isn't optimized for large numbers of small files, as I recall. I can't comment on reliability/performance. I don't know much about JFS either - XFS seems to be receiving more development attention from Red Hat and elsewhere at the moment. I don't think Reiser 3 is seeing much work anymore either.
XFS has had FSCK problems in the past. I think that JFS is as good as dead. Even before Hans was arrested there were some issues with ReiserFS such as the fact that hostile data written to a file by a user could cause a corruption at FSCK time. If you use ReiserFS for any server that allows binary data to be stored by a user then you risk security problems. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/