On Thu, Feb 02, 2012 at 08:46:55AM +0100, Alessio Cecchi wrote:
How many users there are in this installation?
Quite a few :-) This is for an ISP.
The active servers are using Maildir, and has:
$ df -h /usr/local/atmail/users/ Filesystem Size Used Avail Use% Mounted on /dev/atmailusers 14T 12T 2.2T 85% /usr/local/atmail/users $ df -hi /usr/local/atmail/users/ Filesystem Inodes IUsed IFree IUse% Mounted on /dev/atmailusers 145M 113M 33M 78% /usr/local/atmail/users
very little of this is compressed (zlib plugin enabled during christmas).
This is the old storage in Maildir format?
Correct.
I'm surprised that the destination server is so large, was expecting zlib and mdbox and SIS would compress it down to much less than what we're seeing (12TB -> 5TB):
$ df -h /srv/mailbackup Filesystem Size Used Avail Use% Mounted on /dev/mapper/mailbackupvg-mailbackuplv 5.7T 4.8T 882G 85% /srv/mailbackup
This is the new storage in mdbox format?
Correct.
What size you would expect?
With Maildir I see message-files shrink to about 20%* of original size after turning on zlib with zlib_save_level=6. I was expecting better compression with mdbox (and zlib_save_level=9), and I would expect SIS to help even further.
mdbox+SIS+zlib_save_level=9 variant taking up 40% the space of a mixed** compressed/non-compressed Maildir storage isn't very impressive to me -- and the mdbox backup isn't even complete (it's only the 25% most active users).
Yes, I see there might be holes in my logic, expecting compressed messages to compress further after move to mdbox. But also I have expectation that most of the messages are not already compressed on the Maildir side. Sorry, expectations and guesses, not hard facts.
[*] based on a couple of samples, not thourough research [**] Only messages saved after we enabled zlib on December 25. are compressed.
-jf