ZFS continuously growing

[Robert Eckardt]

Hi folks,

after upgrading my backup server to 8.0-BETA2, I noticed that the 
available space shrinks from backup to backup (a tree each day with 
differential rsync) although with each new tree the oldest tree gets 
removed.

Since I removed some subdirectories on my active server the number 
of used inodes now is reduced by approx. 90000 on each run.
At the same time used space grows by between 650MB and 6.7GB and
free space gets reduced by 4.4 to 9GB (see table below). The output 
of "df" and "zfs list" is consistent.

Although I understand that the backed-up file by rsync can be much 
larger than the data transferred I get worried that without changing 
much the available space shrinks continuously. (Remember, the number 
of backup trees stays constant since the oldest gets removed and 
6GB/d results in more that 1TB over half a year.)

Do I have to be worried?
Is there a memory leak in the current ZFS implementation?
Why is used space growing slower than free space is shrinking?
Is there some garbage collection needed in ZFS?

Besides, although the backup server has 3 GB RAM I had to tune arc_max 
to 150MB to copy the backed-up data from an 2.8TB ZFS (v6) to the 
4.5 TB ZFS (v13) by "zfs send|zfs recv" without kmalloc panic.
(I.e., the defaults algorithm was not sufficient.)

Regards,
Robert

day	rsynced		Used		free		inodes		oldest dir	newest dir	d-used		d-free		d-inode
27	57018987	2792986368	1914681984	43854571	20090224-0917	20090827-0916			
28	67181251	2794269440	1910242176	43765134	20090225-0917	20090828-0916
1.283.072	-4.439.808	-89.437
30	52078382	2800983296	1897022720	43586320	20090227-0917	20090830-0916
6.713.856	-13.219.456	-178.814
31	2647268060	2803757056	1891064192	43496712	20090228-0917	20090831-0916
2.773.760	-5.958.528	-89.608
1	92096258	2804415616	1881965184	43406059	20090301-0917	20090901-0916
658.560		-9.099.008	-90.653
2	121590303	2807900288	1875341440	43316517	20090302-0917	20090902-0916
3.484.672	-6.623.744	-89.542

--
Dr. Robert Eckardt    ---    Robert.Eckardt at Robert-Eckardt.de