mksnap_ffs time
Daan Vreeken [PA4DAN]
Danovitsch at vitsch.net
Thu Jan 3 15:21:27 PST 2008
Hi Hackers,
I'm running a 6.2-RELEASE server with a /home partition that's used to backup
a customer's data. The backups are being made during the night. Since a
couple of weeks I'm running mksnap_ffs daily to create filesystem snapshots
of the data. I've been logging the time it takes mksnap_ffs to create it's
snapshot. Here are the 'time' numbers for the last 11 days :
1696.25 real 0.00 user 16.55 sys
1884.09 real 0.00 user 18.63 sys
2038.50 real 0.00 user 20.72 sys
2354.69 real 0.00 user 25.07 sys
2202.43 real 0.00 user 23.08 sys
2621.88 real 0.00 user 27.46 sys
2791.46 real 0.00 user 29.57 sys
2845.48 real 0.00 user 31.69 sys
2894.24 real 0.00 user 32.60 sys
3085.37 real 0.00 user 35.62 sys
3253.11 real 0.00 user 37.25 sys
Right now the filesystem contains 'just' 16 snapshots. The filesystem itself
is a 700GB partition :
# df
Filesystem 1K-blocks Used Avail Capacity Mounted on
...
/dev/twed0s3d 700905640 271350848 373482342 42% /home
The filesystem has been created with default newfs flags. Today the filesystem
contains 186615 files. Average file size is about 140 to 150KB. The data
consists of lots of very small files, lots of middle-sized files, and a bunch
of huge files, so 'average' file size might not be a very good measure.
Every day between 300 to 400MB of data is changed/added. The time it takes to
take another snapshot seems to increase with about 140 seconds a day. If the
snapshot time keeps increasing in this fashion, the server will spend half of
it's time in a day creating snapshots by the end of the year ;-)
1) Is anyone else seeing this?
2) Is there anything that can be done to improve snapshot creation time?
3) Is this something that has already been improved in version X of FreeBSD?
And just for my own curiosity:
Where does mksnap_ffs spend most of it's time? Is this something that simply
can't be changed by the nature of UFS, or is it a known deficiency in the
code that could by improved somehow?
(btw: I can provide more information on the hardware or the filesystem (file
size histograms anyone?) if anyone is interested.)
Thanks for any insights,
--
Daan
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