On Mon, 2004-09-13 at 00:41, Russell Coker wrote: > On Mon, 6 Sep 2004 23:35, Adrian 'Dagurashibanipal' von Bidder > <[EMAIL PROTECTED]> wrote: [...] > Do you have benchmark results to support this assertion? Last time I tested > the performance of software RAID-1 on Linux I was unable to get anywhere near > 2x disk speed for writing. I did tests by reading two files that were 1G in > size and the operation took considerably longer than reading a single 1G file > from a non-RAID system. If RAID-1 was delivering twice the read throughput > then I should be able to read two 1G files concurrently from a RAID-1 in the > same time as would be taken to read a single 1G file from a single disk.
I think Russel must be checking if the class is awake :-) That doesn't sound like a fair test; reading two files at once means the heads have to bounce around all over the place. If you are just talking throughput, then reading a 1G file should take half the time on a RAID-1 that it does on a single disk. I suspect that reading 2 1G files at once on RAID-1 will be not much faster than reading 2 1G files on a single disk, because reading two files at once will probably be seek-bound, not throughput bound. RAID-1 boosts throughput, not latency. HDD latency is a killer. It is significantly faster to read small objects from another machine's RAM over ethernet than off the local HDD; HDD latency is ~10ms, ethernet is <1ms. -- Donovan Baarda <[EMAIL PROTECTED]> http://minkirri.apana.org.au/~abo/ -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
