On Mar 22, 2013, at 11:12 AM, Roman Mamedov <rm@xxxxxxxxxx> wrote:
>> The "disk" is an iscsi disk that in my benchmarks performs roughly like a local raid with 2-3 SATA disks.
>
> I think you should re-verify if this is still the case. Maybe your block
> device performance suddenly plummeted for some other unrelated issue?
>
> The simplest test would be "hdparm -t /dev/sdc".
If I boot without mounting the btrfs file system then I get:
Timing buffered disk reads: 268 MB in 3.01 seconds = 89.14 MB/sec
Timing buffered disk reads: 268 MB in 3.02 seconds = 88.86 MB/sec
Timing buffered disk reads: 268 MB in 3.01 seconds = 89.18 MB/sec
Timing buffered disk reads: 266 MB in 3.00 seconds = 88.59 MB/sec
Timing buffered disk reads: 272 MB in 3.01 seconds = 90.26 MB/sec
Timing buffered disk reads: 268 MB in 3.01 seconds = 88.99 MB/sec
Timing buffered disk reads: 266 MB in 3.01 seconds = 88.48 MB/sec
I also made a new LUN on the iscsi target and tested with bonnie++ on a fresh btrfs file system on that device and got reasonable results (mounted without compression to make sure that wouldn't make it cheat on actual IO):
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
gunnarr.bn.d 15456M 476 99 122194 13 42724 8 2327 95 113553 14 494.8 21
Latency 44109us 465ms 268ms 19309us 300ms 1161ms
Version 1.96 ------Sequential Create------ --------Random Create--------
gunnarr.bn.dev -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 14550 57 +++++ +++ 20353 67 15617 61 +++++ +++ 19165 72
Latency 295us 566us 532us 373us 29us 561us
For what it's worth the iscsi target (a Synology box, some sort of linux) shows lower load running bonnie++ than when the other btrfs file system is mounted with the btrfs-cleaner process running (and nothing happening).
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