zfs discuss - Oct 2010 - Good write, but slow read speeds over the network

Hi all,

I am running Netalk on OSol snv134 on a Dell R610, 32 GB RAM server. I 
am experiencing different speeds when when writing to and reading from 
the pool.
The pool itself consists of two FC LUNs that each build a vdev (no 
comments on that please, we discussed that already! ;) ).

Now, I am having a couple of AFP clients that access this pool either 
via FastEthernet or even GiBitEthernet. The point is: write to these AFP 
shares are pretty fast. Due to the fairly hight amount of RAM I am 
getting transfer speeds of up to 90 MB/sec for a 5 GB file, which is not 
bad. But reading from the pool seems to pan out at 40 to 50 MB/sec. no 
matter what I am trying.

When I run zpool iostat <pool> 1 while reading a big file from the 
share, I can see that the pool has continous reads of about 50 to 60 
MB/sec. and I am getting approx. 30 MB/sec on the client. Afterwards the 
files must reside in the ZFS file cache, since readint he same file 
again, will not show any read activity on the pool at all, but the 
transfer rate is still quite slow  - a max. of 45 to 50 MB/sec.

When I use dd on the host itself to copy the file from the pool to 
/dev/null I am getting approx. 120 MB/sec, which is still way more than 
the 30 to 50 MB/sec I am getting over the network. If I use nc on the 
server, I will get approx 200 MB/sec, so the pool seems to be fast enough.

I was wondering if there''s anything related to ZFS, that could help 
here, or is it more likely a network related issue?

Cheers,
budy

-- 
Stephan Budach
Jung von Matt/it-services GmbH
Glash?ttenstra?e 79
20357 Hamburg

Tel: +49 40-4321-1353
Fax: +49 40-4321-1114
E-Mail: stephan.budach at jvm.de
Internet: http://www.jvm.com

Gesch?ftsf?hrer: Ulrich Pallas, Frank Wilhelm
AG HH HRB 98380

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