On Thu, 5 Apr 2007, Iustin Pop wrote:

On Thu, Apr 05, 2007 at 04:11:35AM -0400, Justin Piszcz wrote:

quoted

On Thu, 5 Apr 2007, Iustin Pop wrote:

quoted

On Wed, Apr 04, 2007 at 07:11:50PM -0400, Bill Davidsen wrote:

quoted

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).

Did you copy it multi-threaded? I said "*multiple-readers* show improved
speed" and you said "I copied *one* file". Try copying two files in
parallel.

I'm doing in two xterms "cat file1 >/dev/null", "cat file2 >/dev/null"
and my raid1 shows ~110 MB/s, each drive doing about half.  On file only
does about 60 MB/s (this is over a PCI raid controller so the max 110
MB/s is a PCI bus limitation).

Iustin
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Ah, nope, I only did a single copy, I did not parallelize the operations.

Justin.