Lorenzo Perone lopez.on.the.lists at yellowspace.net
Fri Oct 31 08:48:28 PDT 2008

> I use ZFS since 7.0-RELEASE. I'm currently using latest stable.
> Ok the load is not as a production one, as the box is used as a home  
> server (NAS), but the hardware is limited too (only 512MB of RAM,  
> mono-core A64 3200+, motherborad integrated sata controler).
> I tried to stress the filesystem a bit with multiple simultaneous  
> rsyncs. No glitches. The only failures was when swap was on a zvol  
> instead of the system drive. Even with more ram, it regularely ended  
> in panics or deadlocks (most of the time, deadlocks) under "high"  
> load.
> Not sure of anything here, but you might want to try with non-zfs  
> swap - on another drive(s) or dedicated slices ?

Yep, I think I'm going to use a separate slice
for the pool, mounting into the respective jails
only the needed filesystems:

mypool/mail into /jails/mail/maildataroot
mypool/db into /jails/web/mysql-bup-slave

(or sort of)

and then use frequent snapshots for mypool/mail
(even hourly or so), and for the database,
a few times per day mysql-backup-slave.sh stop,
zfs snapshot mypool/db, mysql-backup-slave.sh start..

the mysql slave snapshotting is really a goodness
which I've used on a SunOS with zfs and really
rocks. So I never shutdown the master, the slave
goes down only a few seconds, and the database
filesystem is consistent and synced.

In the current case, I think it is not only a feature
but also a must: _If_ the host deadlocks and
mysql fails to sync, at least I have a working
snapshot of the data. I wouldn't put the master itself
on zfs for now, but if all goes well for a while,
why not.

BTW: while sync does not work anymore in a deadlock situation,
I've seen that fsync mostly still does.
So something like find /var/db/mysql -type f -exec fsync {} \;
can save your files if the db is running on UFS..

Thanx & Regards!


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