* Michael Tokarev (mjt@xxxxxxxxxx) wrote:
<snip>
> By the way, I did some testing of various drives, and NCQ/TCQ indeed
> shows some difference -- with multiple I/O processes (like "server"
> workload), IF NCQ/TCQ is implemented properly, especially in the
> drive.
>
> For example, this is a good one:
>
> Single Seagate 74Gb SCSI drive (10KRPM)
>
> BlkSz Trd linRd rndRd linWr rndWr linR/W rndR/W
<snip>
> 1024k 1 83.1 36.0 55.8 34.6 28.2/27.6 20.3/19.4
> 2 45.2 44.1 36.4/ 9.9
> 4 48.1 47.6 40.7/ 7.1
>
> The tests are direct-I/O over whole drive (/dev/sdX), with
> either 1, 2, or 4 threads doing sequential or random reads
> or writes in blocks of a given size. For the R/W tests,
> we've 2, 4 or 8 threads running in total (1, 2 or 4 readers
> and the same amount of writers). Numbers are MB/sec, as
> totals (summary) for all threads.
>
> Especially interesting is the very last column - random R/W
> in parallel. In almost all cases, more threads gives larger
> total speed (I *guess* it's due to internal optimisations in
> the drive -- with more threads the drive has more chances to
> reorder commands to minimize seek time etc).
>
> The only thing I don't understand is why with larger I/O block
> size we see write speed drop with multiple threads.
My guess is that something is chopping them up into smaller writes.
> And in contrast to the above, here's another test run, now
> with Seagate SATA ST3250620AS ("desktop" class) 250GB
> 7200RPM drive:
>
> BlkSz Trd linRd rndRd linWr rndWr linR/W rndR/W
<snip>
> 1024k 1 78.4 34.1 33.5 24.6 19.6/19.5 16.0/12.7
> 2 33.3 24.6 15.4/13.8
> 4 34.3 25.0 14.7/15.0
>
<snip>
> And second, so far I haven't seen a case where a drive
> with NCQ/TCQ enabled works worse than without. I don't
> want to say there aren't such drives/controllers, but
> it just happen that I haven't seen any.)
Yes you have - the random writes with large blocks and 2 or 4 threads
is significantly better for your non-NCQ drive; and getting more
significant as you add more threads - I'm curious what happens
on 8 threads or more.
Dave
--
-----Open up your eyes, open up your mind, open up your code -------
/ Dr. David Alan Gilbert | Running GNU/Linux on Alpha,68K| Happy \
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\ _________________________|_____ http://www.treblig.org |_______/
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