Quick ZFS Question - Writing

L

ldoodle

Limp Gawd
Joined
Jun 29, 2011
Messages
172
Hiya,

I have 6 mirrors in my data pool made up of 7200RPM 2t drives, with each disk in each mirror split across 2 controllers.

When monitoring 'zpool iostat -v poolname 2' during an intensive write (1.3t from a USB drive connected to a PC, copying over the 1 gig LAN), 5 of the iterations would be zeroed out (all columns at zero), but the 6th one would be like ~150MB write, then back to 5 zeroed out.

Windows is reporting the write speed as 25MB/s. This seems slow to me but I guess it's the USB 2 interface slowing it down (which maxes out a 480Mb/s)

So just wondering how ZFS actually 'commits' data to disk, and if what I am seeing is correct. 'iostat -exmn' shows no errors.
 
Sounds about right,

You haven't told us your system specs, but from a USB drive over LAN to system with ZFS 20mb is pretty good

USB is 480 mega BITS /s so equal to about 30 mega BYTES a sec thruput MAX;)

.
 
ldoodle said:
Windows is reporting the write speed as 25MB/s.
Click to expand...

Are you viewing 25MB/s in taskmgr.exe? That number is less accurate than if you were to set up a perfmon configured for your NIC.
 
Stanza33 said:
Sounds about right,

You haven't told us your system specs, but from a USB drive over LAN to system with ZFS 20mb is pretty good

USB is 480 mega BITS /s so equal to about 30 mega BYTES a sec thruput MAX;)

.
Click to expand...

Specs are Quad Core Opteron, 8GB ECC RAM, LSI 3081E-R (1068E controller)

I know USB is 480 mega bits, which is why I put a small b (Mb rather than MB) ;)
 
That looks perfectly normal. The USB can only read ~30mB/sec, and because ZFS is copying and it's not a sync write, it just keeps the data in ram until it wants to flush it all to disk in one big write. Everything is fine..
 
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