[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-users] xen disk io performance
Am Dienstag, 29. November 2011, 14:10:45 schrieb Jeff Sturm: > Mechanical disks are slow. The rules for disk performance haven't really > changed due to virtualization: lots of RAM, lots of buffering. ack > In other words, avoid disk accesses like the plague. Especially random I/O > to physical drives. ack. > Solid-state storage helps, but you can often achieve the same effect with > lots of RAM, on the cheap. This is not correct in all cases as this still hardly depends from the model (wear leveling etc.) and - not at least - the applications disk usage profile (i.e. hardly parallel accesses etc.). This means: a high quality and application specific optimized SAS RAID could be significantly "faster" then many SSDs. > random I/O is still the problem, which can only be mitigated with more spindles (we'd normally have at least 2 per physical host, but in our virtual cluster we've allocated one-fourth of that). yes, but just additionally: a "long" SAN path could slow down random i/o transaction rates too comparing to "directly" attached disks. Another "ugly" point on SAN could be parallel access from other users / SAN clients to the same physical disks or even swapping onto it from the same systems. > Two, rotating media are 1970's technology, good for little more than archival, ripe for replacement. I'm keeping an eye on price/capacity for solid state storage. SSDs are still not a generally better / faster solution (even if you did not rely on the price) in each case - especially in database situations. Most database software developers / projects are still developing / optimizing their products for SSD storage usage as over decades for rotating disks before and the manufacturers of SSDs do their part of the development. See i.e. developer discussions on MySQL etc. about this topic... hth best regards, Niels. -- --- Niels Dettenbach Syndicat IT&Internet http://www.syndicat.com/ Attachment:
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