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Slow read, fast write after tricky raidz2 creation.

Z

zsozso

n00b
Joined
Apr 21, 2011
Messages
10
I've made a 10 disk raidz2 pool with 8 drives(the last 2 drives had the data from my previous pool) and 2 md devices.
(The pool was made with using the gnop trick so It should not be an allignment problem.)
After creating the pool I've removed the md devices so the pool became degraded but still usable. I've copied all my data from the ramaining two disks, then replaced the 2 remaining unavailable devices with them. The raid was resilvered in about 2x5h and all was fine.

I've tried to benchmark the pool in the degraded state with only 8 drives, and I got ~800MB/s read 600MB/s write. After rebuilding the pool now I have 300-600MB/s read and 500-600MB/s write, which is not too terrible but It should be faster than in the degraded state.
I've checked with gstat and my suspicion was right. The last two drives are 99% busy and the rest of the drives are 40-60% busy.
My configuration:
pool: tank
state: ONLINE
scan: resilvered 48K in 0h0m with 0 errors on Mon Apr 2 18:37:06 2012
config:

NAME STATE READ WRITE CKSUM
tank ONLINE 0 0 0
raidz2-0 ONLINE 0 0 0
gpt/tank3 ONLINE 0 0 0
gpt/tank5 ONLINE 0 0 0
gpt/tank6 ONLINE 0 0 0
gpt/tank9 ONLINE 0 0 0
gpt/tank10 ONLINE 0 0 0
gpt/tank7 ONLINE 0 0 0
gpt/tank8 ONLINE 0 0 0
gpt/tank4 ONLINE 0 0 0
gpt/tank1 ONLINE 0 0 0
gpt/tank2 ONLINE 0 0 0

zdb tank | grep ashift
ashift: 12

Cpu: g530
MB: Gigabyte z68
Ram: 16GB
Controller: m1015 IT firmware
Disks: 10xSamsung F4 204UI

Last night for some reason the pool performed optimally:
Pool : tank (18.1T, 27% full)
Test size : 64 GiB
Data source : /dev/zero
Read throughput : 911.2 MB/s = 869 MiB/s
Write throughput: 559.1 MB/s = 533.2 MiB/s

Unfortunately I had to reboot and after that I get these numbers:
Pool : tank (18.1T, 27% full)
Test size : 64 GiB
Data source : /dev/zero
Read throughput : 577 MB/s = 550.3 MiB/s
Write throughput: 537.7 MB/s = 512.7 MiB/s

If you have an idea please share it with me.
 
Last edited:
Well it seems I'm not getting any further in finding a sollution.

I've tried almost everything now, recreating the pool in all kind of ways, tuning and such, but I still cannot reproduce those sweet numbers.

I even tried to install openidiana but it only brought me bitter dissapointment. (Much slower than bsd)

The only somewhat effective tuning options are min/max pending and aggregation.
I've tried to make 2 raid0 arrays with 5 disks in each of them just to find out if there is a bad disk, but it seems that the disks are almost identical in speed.

Raid0 pool1:
ZFSguru 0.2.0-beta5 pool benchmark
Pool : storage1 (9.06T, 0% full)
Test size : 64 GiB
Data source : /dev/zero
Read throughput : 551.6 MB/s = 526 MiB/s
Write throughput: 481.7 MB/s = 459.3 MiB/s

Raid0 pool2:
ZFSguru 0.2.0-beta5 pool benchmark
Pool : storage2 (9.06T, 0% full)
Test size : 64 GiB
Data source : /dev/zero
Read throughput : 567.7 MB/s = 541.4 MiB/s
Write throughput: 545.7 MB/s = 520.4 MiB/s

My main problem is the read performance, sometimes the write is faster than the read.
Afaik it should be higher when using raidz2.

Now testing RAIDZ2 configuration with 10 disks: cWmRzmId@
READ: 590 MiB/sec = 590 MiB/sec avg
WRITE: 576 MiB/sec = 576 MiB/sec avg

Any idea would help me greatly,
zsozso
 
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