Don't forget that often controlers don't obey fsyncs like a plain drive does. thats the point of having a BBU ;)
Alex Turner NetEconomist On 8/16/05, John A Meinel <[EMAIL PROTECTED]> wrote: > Anjan Dave wrote: > > Yes, that's true, though, I am a bit confused because the Clariion array > > document I am reading talks about how the write cache can eliminate the > > RAID5 Write Penalty for sequential and large IOs...resulting in better > > sequential write performance than RAID10. > > > > anjan > > > > To give a shorter statement after my long one... > If you have enough cache that the controller can write out big chunks to > the disk at a time, you can get very good sequential RAID5 performance, > because the stripe size is large (so it can do a parallel write to all > disks). > > But for small chunk writes, you suffer the penalty of the read before > write, and possible multi-disk read (depends on what is in cache). > > RAID10 generally handles small writes better, and I would guess that > 4disks would perform almost identically to 6disks, since you aren't > usually writing enough data to span multiple stripes. > > If your battery-backed cache is big enough that you don't fill it, they > probably perform about the same (superfast) since the cache hides the > latency of the disks. > > If you start filling up your cache, RAID5 probably can do better because > of the parallelization. > > But small writes followed by an fsync do favor RAID10 over RAID5. > > John > =:-> > > > ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
