Don't forget about max_sectors_kb either (for all drives in the SW RAID5
array)
max_sectors_kb = 8
$ dd if=/dev/zero of=file.out6 bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 55.4848 seconds, 194 MB/s
max_sectors_kb = 16
$ dd if=/dev/zero of=file.out5 bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 37.6886 seconds, 285 MB/s
max_sectors_kb = 32
$ dd if=/dev/zero of=file.out4 bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 26.2875 seconds, 408 MB/s
max_sectors_kb = 64
$ dd if=/dev/zero of=file.out2 bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 24.8301 seconds, 432 MB/s
max_sectors_kb = 128
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 22.6298 seconds, 474 MB/s
On Sun, 24 Jun 2007, Dr. David Alan Gilbert wrote:
* 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 \
\ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
\ _________________________|_____ http://www.treblig.org |_______/
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