On Thu, 5 Apr 2007, Justin Piszcz wrote:
On Thu, 5 Apr 2007, Iustin Pop wrote:
On Wed, Apr 04, 2007 at 07:11:50PM -0400, Bill Davidsen wrote:
You are correct, but I think if an optimization were to be done, some
balance between the read time, seek time, and read size could be done.
Using more than one drive only makes sense when the read transfer time is
significantly longer than the seek time. With an aggressive readahead set
for the array that would happen regularly.
It's possible, it just takes the time to do it, like many other "nice"
things.
Maybe yes, but why optimise the single-reader case? raid1 already can
read in parallel from the drives when multiple processes read from the
raid1. Optimising the single reader can help in hdparm or other
benchmark cases, but in real life I see very often the total throughput
of a (two drive) raid1 being around two times the throughput of a single
drive.
regards,
iustin
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Really? I have copied a file from a SW RAID1 (5GB) and I only saw 60MB/s not
the 120MB/s the (RAID1) is capable of to the destination (which can easily do
160MB/s sustained read/write).
Justin.
Using 2 threads made no difference either.
It was not until I did 3 simultaneous copies that I saw 110-130MB/s
through vmstat 1, until then, it only used one drive, even with two cp's,
how come it needs to be three or more?
Justin.
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