what "wrt" stands for ? On 12/29/05, Mark Overmeer <[EMAIL PROTECTED]> wrote: > * Raz Ben-Jehuda(caro) ([EMAIL PROTECTED]) [051229 10:10]: > > I have tested the overhead of linux raid0. > > I used two scsi atlas maxtor disks ( 147 MB) and combined them to single > > raid0 volume. > > The raid is striped in 256K stripes. > > Are you sure you tested "linux" overhead? Maybe you have just tested raid0 > properties. > > > I filled the raid0 up to the maximum with files over xfs file system. > > I've checked the peformance of reading 60 files like that: > > > > while need to read > > for every file > > read 0.5 M from file > > > > I got 50 MB/s . > > > > Armed with this knowledge i went and did the same test over > > one disk and i got 32 MB/s . > > > > Question: > > why is this perfomance drop ? > > Good performance for such small reads wrt the block-size... > Ok, simple calculation: > seek time average for one disk is half a rotation > for two disks 1 - (1-0.5)*(1-0.5) = 0.75 rotation > > Without taking into account the time to do actual reads: > 0.5/0.75 * (2x32MB/s) = 43MB/s (34% performance drop) > > The only effect you see is that the probability that both disks are in > optimal position to read from them decreases. > > Solution: take very large files wrt the stripe-size to get double > performance. Or take files smaller than the stripe-size. > > Of course, there can be other reasons which can reduce the performance > as well. However, I achieve 200MB/s over 4 striped disk each capable > of 50MB/s for huge files and 64K stipes... Linux doesn't seem to be the > bottleneck in my setup. > -- > Regards, > MarkOv > > ------------------------------------------------------------------------ > Mark Overmeer MSc MARKOV Solutions > [EMAIL PROTECTED] [EMAIL PROTECTED] > http://Mark.Overmeer.net http://solutions.overmeer.net > >
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