On Tue, Jul 28, 2009 at 3:56 PM, Kenneth Marshall <k...@rice.edu> wrote:
> Kage, > > The main advantage is gained by avoiding I/O through the virtual > disk. The layout of the virtual disk tends to turn most I/O into > random I/O, even I/O that starts as sequential. The factor of > 10 performance difference between random/sequential I/O causes > the majority of the performance problem. I have not had personal > experience with using an NFS mount point to run a database so I > cannot really comment on that. Good luck with your evaluation. > You're trading head-seeking latencies for network latencies, and those are almost certainly higher. Hosting your database server binaries and such forth in NFS is possible, though again, not optimal both from a performance and risk standpoint (NFS server drops, your DB binaries vanish, your DB server drops even though the machine hosting it was fine). I think hosting databases in NFS can cause serious problems - I seem to remember older versions of mysql wouldn't support that. I don't know if newer ones do...but I do know in the *very large* IT environment I worked in, all database servers hosted the DBs on their local disks or in filesystems hosted on disks (SANS?) attached via fibre-channel. Could solid-state drives side-step the random-access issue with virtualization, or at least make it suck less? Based on how many people I know who have said "Wow, my SSD died. I thought those were supposed to be more reliable?" ... I wouldn't bet my service uptime on it. ;) -Rob
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