On Sat, April 20, 2013 17:38, Jarry wrote: > On 20-Apr-13 17:00, Tanstaafl wrote: > >> Another question - are there any caveats as to which filesystem to use >> for a mail server, for virtualized systems? Ir do the same >> issues/questions apply (ie, does the fact that it is virtualized not >> change anything)? > > Problem of virtualized filesystem is not that it is virtualized, > but that it is located on datastore with more virtual systems, > all of them competing for the same i/o. *That* is the bottleneck. > If you switch reiser for xfs or btrfs, you might win (or loose) > a few %. If you optimize your esxi-datastore design, you might > win much more than what you have ever dreamed of.
If the underlying I/O is fast enough with low seek-times and high throughput, that handling multiple VMs using a lot of disk I/O simultaneously isn't a problem. Provided the Host has sufficient resources (think memory and dedicated CPU) to handle it. > I have 8 VMs (out of them 6 are Gentoo) hosted on ESXi, intended > for various tasks (mail, dns, mysql, web, etc), moderately loaded. > I used hw-raid controller with 2x sata-hdd in raid1 but performance > was quite dissapointing and I experienced all sorts of i/o jams. Which hw-raid controller did you use? RAID-1 (mirroring) isn't actually known for high performance. > Then I switched hdd for ssd (yes I use 2 of them in raid1, even > if this is not generally recommended) and performance rocks now! > I can start now kernel compilation on all 6 VMs at the same time, > with near-zero performance penalty (depending on cpu/vcpu ratio > and number of threads used). Unthinkable with hdd-based datastore. I have HDD-based datastores and can do this on 4 VMs (single quad-core CPU) without any penalty. > I would definitely recommend using SSD. Either directly as > datastore for VMs, or at least as EXSi host-cache. There is > also possibility of "hybrid-raid" (1xSSD and 1xHDD in raid1) > on some raid-controllers. Or if your pocket is really deep, > you could grab one of those FusionIO-cards to avoid being > limited by rather slow sata-interface (SSD for PCIe)... A decent hardware raid-controller with multiple disks running in a higher raid version is cheaper then the same storage capacity in SSDs. -- Joost
