On Sun, Oct 14, 2012 at 7:25 PM, Russell Coker <[email protected]> wrote: > I'm looking at converting some Xen servers to ZFS. This includes a couple of > servers for a reasonable size mail store (8,000,000 files and 600G of Maildir > storage). > > For much of the Xen on ZFS stuff I'll just use zvols for block devices and > then use regular Linux filesystems such as Ext3 inside them. This isn't > particularly efficient but for most DomUs it doesn't matter at all. Most of > the DomUs have little disk access as they don't do much writing and have > enough cache to cover most reads. > > 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. > 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. 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. -- Daniel Pittman ♲ Made with 100 percent post-consumer electrons _______________________________________________ luv-main mailing list [email protected] http://lists.luv.asn.au/listinfo/luv-main
