Date: Wed, 19 May 2010 10:27:09 +0200 From: Arnaud Houdelette <tzim@tzim.net> To: freebsd-fs@freebsd.org Subject: ZFS Recordsize tuning & transmission (bittorent daemon) Message-ID: <4BF3A0DD.4080404@tzim.net>
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Hi,
I'm using the transmission bittorent client on a single drive ZFS pool
(name unsafe). Downloading is mostly OK.
But moving a downloaded file to an other zpool (zraid, name tank) takes
ages.
The pools :
[carenath] ~> zpool status
pool: tank
state: ONLINE
scrub: none requested
config:
NAME STATE READ
WRITE CKSUM
tank ONLINE
0 0 0
raidz1 ONLINE
0 0 0
gptid/ffb4e96a-d497-11de-96bd-001d923bc7a0 ONLINE
0 0 0
gptid/9fb111f8-d426-11de-99bc-001d923bc7a0 ONLINE
0 0 0
gptid/0902db4e-d462-11de-96bd-001d923bc7a0 ONLINE
0 0 0
gptid/e3838ce5-d4ed-11de-96bd-001d923bc7a0 ONLINE
0 0 0
errors: No known data errors
pool: unsafe
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
unsafe ONLINE 0 0 0
ad0p3 ONLINE 0 0 0
errors: No known data errors
zpool iostat during the move shows :
zpool iostat 5
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
tank 2.65T 77.7G 6 8 9.65K 346K
unsafe 28.4G 118G 14 10 1.77M 214K
---------- ----- ----- ----- ----- ----- -----
tank 2.65T 77.7G 88 0 131K 0
unsafe 28.4G 118G 76 11 9.28M 114K
---------- ----- ----- ----- ----- ----- -----
tank 2.65T 77.7G 102 46 147K 2.53M
unsafe 28.4G 118G 79 6 9.81M 34.0K
---------- ----- ----- ----- ----- ----- -----
tank 2.65T 77.6G 2 42 4.30K 2.08M
unsafe 28.4G 118G 81 3 10.1M 173K
---------- ----- ----- ----- ----- ----- -----
Why is there 10MB reads on source pool where only ~3MB are written on
destination ?
ZFS recordsize on both pools are default (128k). But as transmission
bittorrent client has no write (nor read) cache, it could mean that data
is written is smaller chunks during download. Could this lead to data
being stored in many not-full records ? Does those unfull records would
have to be read as whole (128k) during the move, which would explain the
above difference on read/write ?
I'm just making assumptions here, as my understanding of internals of
ZFS is limited. Some insights would be appreciated.
Thanks.
Arnaud Houdelette
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