sysinstall, GJOURNAL and ZFS

[Chris Dillon]

Quoting Dmitry Morozovsky <marck at rinet.ru>:

> Well, I can see at least one rather big problem with bgfsck (or with  
> snapshots to be more precise): inappropriate time of file system  
> lock on snapshot creation. On not-too-big 300G ufs2 not-too-heavy  
> loaded snapshot creation time is 20+ minutes, and 5+ from that file  
> system blocked even on reads.  This looks unacceptable for me for  
> any real use.

The snapshot time depends heavily on the I/O throughput of your disk  
subsystem.  On a several year old system with 5 x 72GB 15KRPM U320  
SCSI drives in a RAID5 array, a fairly well loaded 260GB filesystem  
(90GB used, 354K out of 8M inodes used, and several hundred MB to a GB  
of changes per day) completes a snapshot in exactly 2 minutes.  2  
minutes is still too long to be blocking I/O in the middle of the day  
when it is being actively used, so I just take 1 snapshot per day  
while it is idle.  I would love to put ZFS on this system so that I  
could have finer grained snapshots, but I need user quota support  
which our ZFS currently lacks.

-- 

Chris Dillon - NetEng/SysAdm
Reeds Spring R-IV School District
Technology Department
175 Elementary Rd.
Reeds Spring, MO  65737
Voice: 417-272-8266   Fax: 417-272-0015