zfs discuss - Dec 2007 - Performance writing to USB drive, performance reporting

So I''m doing an rsync between a ZFS filesystem on local SATA disks and 
an empty ZFS filesystem on a drive connected via USB 2.0.   zpool iostat 
is showing me a write bandwidth of about 30M.  That does mean 30MB/sec, 
right?  That''s compatible with how long the test took.

I used up 47368826 blocks, du -s says here, or about 24GB.  It took just 
under 14 minutes, so 28MB/s rounded to whole numbers. 

USB 2 is nominally 480 Mbits/s, which is 60Mbytes/sec, and one doesn''t 
expect to achieve nominal performance from disks connected via USB.   So 
if I''m getting 28MB/sec, half nominal, is that about the best I can 
expect?  Or is that poor?  Disks themselves can do, what, 50MB/sec to 
80MB/sec (this is definitely not a 10k or 15k rpm drive here)?  The disk 
in this box is an old PATA; would I be likely to notice the difference 
with a modern SATA in a modern USB case?

How much better would Firewire 400 be?  How much does it depend on the 
controller?  My M2n-sli-deluxe motherboard has IEEE 1394, and there are 
some hits on "1394" in syslog during startup, so that looks vaguely 
hopeful.

I''m not unhappy with backing up 24GB in 14 minutes, all in all.

-- 
David Dyer-Bennet, dd-b at dd-b.net; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

USB2 giving you ~30MB/s is normal... a little better than mine (on Windows -
~25MB/s) actually.

For better performance better switch to eSATA or Firewire. Even FW400 will give
you better results than USB as there are lesser overheads.

However, I''m sure I saw some FW+ZFS related bug in bugdb sometime ago.
Please check.
 
 
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