Hello Roch,
Saturday, June 28, 2008, 11:25:17 AM, you wrote:
RB> I suspect, a single dd is cpu bound.
I don't think so.
Se below one with a stripe of 48x disks again. Single dd with 1024k
block size and 64GB to write.
bash-3.2# zpool iostat 1
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
test 333K 21.7T 1 1 147K 147K
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 0 0 0
test 333K 21.7T 0 1.60K 0 204M
test 333K 21.7T 0 20.5K 0 2.55G
test 4.00G 21.7T 0 9.19K 0 1.13G
test 4.00G 21.7T 0 0 0 0
test 4.00G 21.7T 0 1.78K 0 228M
test 4.00G 21.7T 0 12.5K 0 1.55G
test 7.99G 21.7T 0 16.2K 0 2.01G
test 7.99G 21.7T 0 0 0 0
test 7.99G 21.7T 0 13.4K 0 1.68G
test 12.0G 21.7T 0 4.31K 0 530M
test 12.0G 21.7T 0 0 0 0
test 12.0G 21.7T 0 6.91K 0 882M
test 12.0G 21.7T 0 21.8K 0 2.72G
test 16.0G 21.7T 0 839 0 88.4M
test 16.0G 21.7T 0 0 0 0
test 16.0G 21.7T 0 4.42K 0 565M
test 16.0G 21.7T 0 18.5K 0 2.31G
test 20.0G 21.7T 0 8.87K 0 1.10G
test 20.0G 21.7T 0 0 0 0
test 20.0G 21.7T 0 12.2K 0 1.52G
test 24.0G 21.7T 0 9.28K 0 1.14G
test 24.0G 21.7T 0 0 0 0
test 24.0G 21.7T 0 0 0 0
test 24.0G 21.7T 0 0 0 0
test 24.0G 21.7T 0 14.5K 0 1.81G
test 28.0G 21.7T 0 10.1K 63.6K 1.25G
test 28.0G 21.7T 0 0 0 0
test 28.0G 21.7T 0 10.7K 0 1.34G
test 32.0G 21.7T 0 13.6K 63.2K 1.69G
test 32.0G 21.7T 0 0 0 0
test 32.0G 21.7T 0 0 0 0
test 32.0G 21.7T 0 11.1K 0 1.39G
test 36.0G 21.7T 0 19.9K 0 2.48G
test 36.0G 21.7T 0 0 0 0
test 36.0G 21.7T 0 0 0 0
test 36.0G 21.7T 0 17.7K 0 2.21G
test 40.0G 21.7T 0 5.42K 63.1K 680M
test 40.0G 21.7T 0 0 0 0
test 40.0G 21.7T 0 6.62K 0 844M
test 44.0G 21.7T 1 19.8K 125K 2.46G
test 44.0G 21.7T 0 0 0 0
test 44.0G 21.7T 0 0 0 0
test 44.0G 21.7T 0 18.0K 0 2.24G
test 47.9G 21.7T 1 13.2K 127K 1.63G
test 47.9G 21.7T 0 0 0 0
test 47.9G 21.7T 0 0 0 0
test 47.9G 21.7T 0 15.6K 0 1.94G
test 47.9G 21.7T 1 16.1K 126K 1.99G
test 51.9G 21.7T 0 0 0 0
test 51.9G 21.7T 0 0 0 0
test 51.9G 21.7T 0 14.2K 0 1.77G
test 55.9G 21.7T 0 14.0K 63.2K 1.73G
test 55.9G 21.7T 0 0 0 0
test 55.9G 21.7T 0 0 0 0
test 55.9G 21.7T 0 16.3K 0 2.04G
test 59.9G 21.7T 0 14.5K 63.2K 1.80G
test 59.9G 21.7T 0 0 0 0
test 59.9G 21.7T 0 0 0 0
test 59.9G 21.7T 0 17.7K 0 2.21G
test 63.9G 21.7T 0 4.84K 62.6K 603M
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
test 63.9G 21.7T 0 0 0 0
^C
bash-3.2#
bash-3.2# ptime dd if=/dev/zero of=/test/q1 bs=1024k count=65536
65536+0 records in
65536+0 records out
real 1:06.312
user 0.074
sys 54.060
bash-3.2#
Doesn't look like it's CPU bound.
Let's try to read the file after zpool export test; zpool import test
bash-3.2# zpool iostat 1
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
test 64.0G 21.7T 15 46 1.22M 1.76M
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 6.64K 0 849M 0
test 64.0G 21.7T 10.2K 0 1.27G 0
test 64.0G 21.7T 10.7K 0 1.33G 0
test 64.0G 21.7T 9.91K 0 1.24G 0
test 64.0G 21.7T 10.1K 0 1.27G 0
test 64.0G 21.7T 10.7K 0 1.33G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.2K 0 1.27G 0
test 64.0G 21.7T 10.3K 0 1.29G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 9.16K 0 1.14G 0
test 64.0G 21.7T 1.98K 0 253M 0
test 64.0G 21.7T 2.48K 0 317M 0
test 64.0G 21.7T 1.98K 0 253M 0
test 64.0G 21.7T 1.98K 0 254M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.73K 0 221M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.49K 0 191M 0
test 64.0G 21.7T 2.47K 0 317M 0
test 64.0G 21.7T 1.46K 0 186M 0
test 64.0G 21.7T 2.01K 0 258M 0
test 64.0G 21.7T 1.98K 0 254M 0
test 64.0G 21.7T 1.97K 0 253M 0
test 64.0G 21.7T 2.23K 0 286M 0
test 64.0G 21.7T 1.98K 0 254M 0
test 64.0G 21.7T 1.73K 0 221M 0
test 64.0G 21.7T 1.98K 0 254M 0
test 64.0G 21.7T 2.42K 0 310M 0
test 64.0G 21.7T 1.78K 0 228M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.67K 0 214M 0
test 64.0G 21.7T 1.80K 0 230M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 2.47K 0 317M 0
test 64.0G 21.7T 1.73K 0 221M 0
test 64.0G 21.7T 1.99K 0 254M 0
test 64.0G 21.7T 1.24K 0 159M 0
test 64.0G 21.7T 2.47K 0 316M 0
test 64.0G 21.7T 2.47K 0 317M 0
test 64.0G 21.7T 1.99K 0 254M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.73K 0 221M 0
test 64.0G 21.7T 2.48K 0 317M 0
test 64.0G 21.7T 2.48K 0 317M 0
test 64.0G 21.7T 1.49K 0 190M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.81K 0 232M 0
test 64.0G 21.7T 1.90K 0 243M 0
test 64.0G 21.7T 2.48K 0 317M 0
test 64.0G 21.7T 1.49K 0 191M 0
test 64.0G 21.7T 2.47K 0 317M 0
test 64.0G 21.7T 1.99K 0 254M 0
test 64.0G 21.7T 1.97K 0 253M 0
test 64.0G 21.7T 1.49K 0 190M 0
test 64.0G 21.7T 2.23K 0 286M 0
test 64.0G 21.7T 1.82K 0 232M 0
test 64.0G 21.7T 2.15K 0 275M 0
test 64.0G 21.7T 2.22K 0 285M 0
test 64.0G 21.7T 1.73K 0 222M 0
test 64.0G 21.7T 2.23K 0 286M 0
test 64.0G 21.7T 1.90K 0 244M 0
test 64.0G 21.7T 1.81K 0 231M 0
test 64.0G 21.7T 2.23K 0 285M 0
test 64.0G 21.7T 1.97K 0 252M 0
test 64.0G 21.7T 2.00K 0 255M 0
test 64.0G 21.7T 8.42K 0 1.05G 0
test 64.0G 21.7T 10.3K 0 1.29G 0
test 64.0G 21.7T 10.2K 0 1.28G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.2K 0 1.27G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.6K 0 1.32G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 9.23K 0 1.15G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 10.0K 0 1.25G 0
test 64.0G 21.7T 9.55K 0 1.19G 0
test 64.0G 21.7T 10.2K 0 1.27G 0
test 64.0G 21.7T 10.0K 0 1.25G 0
test 64.0G 21.7T 9.91K 0 1.24G 0
test 64.0G 21.7T 10.6K 0 1.32G 0
test 64.0G 21.7T 9.24K 0 1.15G 0
test 64.0G 21.7T 10.1K 0 1.26G 0
test 64.0G 21.7T 10.3K 0 1.29G 0
test 64.0G 21.7T 10.3K 0 1.29G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 8.54K 0 1.07G 0
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 0 0 0 0
^C
bash-3.2# ptime dd if=/test/q1 of=/dev/null bs=1024k
65536+0 records in
65536+0 records out
real 1:36.732
user 0.046
sys 48.069
bash-3.2#
Well, that drop for several dozen seconds was interesting...
Lets run it again without export/import:
bash-3.2# zpool iostat 1
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
test 64.0G 21.7T 3.00K 6 384M 271K
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 2.58K 0 330M 0
test 64.0G 21.7T 6.02K 0 771M 0
test 64.0G 21.7T 8.37K 0 1.05G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 9.64K 0 1.20G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 10.6K 0 1.32G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 9.65K 0 1.21G 0
test 64.0G 21.7T 9.84K 0 1.23G 0
test 64.0G 21.7T 9.22K 0 1.15G 0
test 64.0G 21.7T 10.9K 0 1.36G 0
test 64.0G 21.7T 10.9K 0 1.36G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.7K 0 1.34G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.9K 0 1.36G 0
test 64.0G 21.7T 10.6K 0 1.32G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.7K 0 1.34G 0
test 64.0G 21.7T 10.5K 0 1.32G 0
test 64.0G 21.7T 10.6K 0 1.32G 0
test 64.0G 21.7T 10.8K 0 1.34G 0
test 64.0G 21.7T 10.4K 0 1.29G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 9.15K 0 1.14G 0
test 64.0G 21.7T 10.8K 0 1.35G 0
test 64.0G 21.7T 9.76K 0 1.22G 0
test 64.0G 21.7T 8.67K 0 1.08G 0
test 64.0G 21.7T 10.8K 0 1.36G 0
test 64.0G 21.7T 10.9K 0 1.36G 0
test 64.0G 21.7T 10.3K 0 1.28G 0
test 64.0G 21.7T 9.76K 0 1.22G 0
test 64.0G 21.7T 10.5K 0 1.31G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 9.23K 0 1.15G 0
test 64.0G 21.7T 9.63K 0 1.20G 0
test 64.0G 21.7T 9.79K 0 1.22G 0
test 64.0G 21.7T 10.2K 0 1.28G 0
test 64.0G 21.7T 10.4K 0 1.30G 0
test 64.0G 21.7T 10.3K 0 1.29G 0
test 64.0G 21.7T 10.2K 0 1.28G 0
test 64.0G 21.7T 10.6K 0 1.33G 0
test 64.0G 21.7T 10.8K 0 1.35G 0
test 64.0G 21.7T 10.5K 0 1.32G 0
test 64.0G 21.7T 11.0K 0 1.37G 0
test 64.0G 21.7T 10.2K 0 1.27G 0
test 64.0G 21.7T 9.69K 0 1.21G 0
test 64.0G 21.7T 6.07K 0 777M 0
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 0 0 0 0
test 64.0G 21.7T 0 0 0 0
^C
bash-3.2#
bash-3.2# ptime dd if=/test/q1 of=/dev/null bs=1024k
65536+0 records in
65536+0 records out
real 50.521
user 0.043
sys 48.971
bash-3.2#
Now looks like reading from the pool using single dd is actually CPU
bound.
Reading the same file again and again does produce, more or less,
consistent timing. However every time I export/import the pool during
the first read there is that drop in throughput during first read and
total time increases to almost 100 seconds.... some meta-data? (of
course there are no errors oof any sort, etc.)
>> Reducing zfs_txg_synctime to 1 helps a little bit but still it's not
>> even stream of data.
>>
>> If I start 3 dd streams at the same time then it is slightly better
>> (zfs_txg_synctime set back to 5) but still very jumpy.
>>
RB> Try zfs_txg_synctime to 10; that reduces the txg overhead.
Doesn't help...
[...]
test 13.6G 21.7T 0 0 0 0
test 13.6G 21.7T 0 8.46K 0 1.05G
test 17.6G 21.7T 0 19.3K 0 2.40G
test 17.6G 21.7T 0 0 0 0
test 17.6G 21.7T 0 0 0 0
test 17.6G 21.7T 0 8.04K 0 1022M
test 17.6G 21.7T 0 20.2K 0 2.51G
test 21.6G 21.7T 0 76 0 249K
test 21.6G 21.7T 0 0 0 0
test 21.6G 21.7T 0 0 0 0
test 21.6G 21.7T 0 10.1K 0 1.25G
test 25.6G 21.7T 0 18.6K 0 2.31G
test 25.6G 21.7T 0 0 0 0
test 25.6G 21.7T 0 0 0 0
test 25.6G 21.7T 0 6.34K 0 810M
test 25.6G 21.7T 0 19.9K 0 2.48G
test 29.6G 21.7T 0 88 63.2K 354K
[...]
bash-3.2# ptime dd if=/dev/zero of=/test/q1 bs=1024k count=65536
65536+0 records in
65536+0 records out
real 1:10.074
user 0.074
sys 52.250
bash-3.2#
Increasing it even further (up-to 32s) doesn't help either.
However lowering it to 1s gives:
[...]
test 2.43G 21.7T 0 8.62K 0 1.07G
test 4.46G 21.7T 0 7.23K 0 912M
test 4.46G 21.7T 0 624 0 77.9M
test 6.66G 21.7T 0 10.7K 0 1.33G
test 6.66G 21.7T 0 6.66K 0 850M
test 8.86G 21.7T 0 10.6K 0 1.31G
test 8.86G 21.7T 0 1.96K 0 251M
test 11.2G 21.7T 0 16.5K 0 2.04G
test 11.2G 21.7T 0 0 0 0
test 11.2G 21.7T 0 18.6K 0 2.31G
test 13.5G 21.7T 0 11 0 11.9K
test 13.5G 21.7T 0 2.60K 0 332M
test 13.5G 21.7T 0 19.1K 0 2.37G
test 16.3G 21.7T 0 11 0 11.9K
test 16.3G 21.7T 0 9.61K 0 1.20G
test 18.4G 21.7T 0 7.41K 0 936M
test 18.4G 21.7T 0 11.6K 0 1.45G
test 20.3G 21.7T 0 3.26K 0 407M
test 20.3G 21.7T 0 7.66K 0 977M
test 22.5G 21.7T 0 7.62K 0 963M
test 22.5G 21.7T 0 6.86K 0 875M
test 24.5G 21.7T 0 8.41K 0 1.04G
test 24.5G 21.7T 0 10.4K 0 1.30G
test 26.5G 21.7T 1 2.19K 127K 270M
test 26.5G 21.7T 0 0 0 0
test 26.5G 21.7T 0 4.56K 0 584M
test 28.5G 21.7T 0 11.5K 0 1.42G
[...]
bash-3.2# ptime dd if=/dev/zero of=/test/q1 bs=1024k count=65536
65536+0 records in
65536+0 records out
real 1:09.541
user 0.072
sys 53.421
bash-3.2#
Looks slightly less jumpy but the total real time is about the same so
average throughput is actually the same (about 1GB/s).
>> Reading with one dd produces steady throghput but I'm disapointed with
>> actual performance:
>>
RB> Again, probably cpu bound. What's "ptime dd..." saying ?
You were right here. Reading with single dd seems to be cpu bound.
However multiple streams for reading do not seem to increase
performance considerably.
Nevertheless the main issu is jumpy writing...
--
Best regards,
Robert Milkowski mailto:[EMAIL PROTECTED]
http://milek.blogspot.com
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