Le Tue, 6 May 2014 15:40:37 +0100 (BST)
Steve Brooks <steveb@xxxxxxxxxxxxxxxx> écrivait:
Yes the write speed is very poor.. I am running "bonnie++" again with
your params but no sure how long it will take.
bonnie++ -f -d ./ -n 50
Will thisno be different for our two machines as it seems to generate
other params depending on the size of the RAM. All ours have 64G RAM.
You MUST test with a dataset bigger than RAM, else you're mostly testing
your RAM speed :) If you've got 64 GB, by default bonnie will test with
128 GB of data. The small size probably explains the very fast seek
speed... You're seeking in the RAM cache :)
I disabled write cache on the controller as there is no ZMM flash
backup module and it seems to be advised that way. I could enable it
and try another test to see if that is a contribution to the poor
write performance. I do have "arcconf" on all our adaptec raid
Modern RAIDs need write cache or perform abysmally. Do yourself a
service and buy a ZMM. Without write cache it'll be so slow it will be
nearly unusable, really. Did you see the numbers? your RAID is more
than 12x slower than mine... actually slower than a single disk! You'll
simply fail at filling it up at these speeds.
I have not tuned the IO scheduler, read ahead, and queue length? I
guess I can try this.
echo none > /sys/block/sda/queue/scheduler
echo 1024 > /sys/block/sda/queue/nr_requests
echo 65536 > /sys/block/sda/queue/read_ahead_kb
Will this need to be done after every reboot? I guess it could go in
Yep. You can tweak the settings and try various configurations.
However these work fine for me in most cases (particularly the noop
scheduler). Of course replace sda with the RAID array device or you may
end up tuning your boot drive instead :)
Thanks loads! As you stated it seems to have all been down to having write
cache disabled. The new results from "bonnie++" show that sequential
writes when the "write cach" is enabled have massively improved to
1642324 K/s ...
[root@sraid2v tmp]# bonnie++ -f -d ./ -n 50 -u root
Using uid:0, gid:0.
Create files in sequential order...done.
Stat files in sequential order...done.
Delete files in sequential order...done.
Create files in random order...done.
Stat files in random order...done.
Delete files in random order...done.
Version 1.96 ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
sraid2v 126G 1642324 96 704219 51 2005711 81 529.8 36
Latency 29978us 131ms 93836us 47600us
Version 1.96 ------Sequential Create------ --------Random Create--------
sraid2v -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
50 45494 75 +++++ +++ 58252 84 51635 80 +++++ +++ 53103 81
Latency 15964us 191us 98us 80us 14us 60us
Thanks again Emmanuel for your help!