> -----Original Message----- > From: Guus Leeuw jr. [mailto:Guus.Leeuw@xxxxxxxxxxxxxxx] > Sent: 05 December 2006 15:03 > To: 'Nik Conwell'; 'Cyrus User's Mailing List' > Subject: RE: how to backup a cyrus server? > > Normally, LVM builds a bitmap indicating which raw blocks it has to copy. > If the bit is down, it reads the block from the source, if the bit is > down, > It reads the block from its own buffer area stored in the snapshot. The > copy-before-write technique guarantees validity of both the snap and the > source. > > Now, depending on the implementation, LVM either takes a bit per physical > extend, or per disk block. For sake of calculations, a per disk block > guess is better... ;) > > So 10G source equals 10485760K source. Divide by 4 (normal disk block == > 4K) equals 2621440K. Divide by 8 (every source block needs 1 bit) equals > 327680. 327680K equals 320M. > Now this won't allow the source to be changed, so pop it up to the next > round number, say 1G, and that's all you need. > > Why this more accurate snapshot-sizing? This way you don't have to make > sure your vg always has 10GB available! You can snap with far less than > that! In your situation you can probably still snap all the while the vg > is used for about 62GB... > > I normally use chunks of 200M for my snapshots in an doubling fashion; > that is, if the lvcreate --snapshot -L${size}M fails, I use 400M, then > 800M, etc. > > Just to let you know, > Guus > > > -----Original Message----- > > From: info-cyrus-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:info-cyrus- > > bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Nik Conwell > > Sent: 05 December 2006 14:17 > > To: Cyrus User's Mailing List > > Subject: Re: how to backup a cyrus server? > > > > I chose that number based on scientific total lack of clue. Also, > > that was the nearest round number of space left over in the cyrus VG > > (~68G). I take it I overestimated a little :) > > > > > > On Dec 5, 2006, at 9:02 AM, Guus Leeuw jr. wrote: > > > > > I am just wondering why in the world you are using 10G for your > > > snapshot? > > > This is 10G worth of snapshot bitmap + changes to the source while the > > > snapshot is active. Hence you either have a *large* source, or a very > > > *active* mail system...? > > > > > > Just my $0.02, > > > Guus > > > > > >> -----Original Message----- > > >> From: info-cyrus-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:info-cyrus- > > >> bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Nik Conwell > > >> Sent: 05 December 2006 12:05 > > >> To: Cyrus User's Mailing List > > >> Subject: Re: how to backup a cyrus server? > > >> > > >> ctl_mboxlist -d for a text mailboxes file, ctl_cyrusdb -c to > > >> checkpoint, a sync, and then a lvcreate --snapshot --size 10G --name > > >> lv_cyrus_snapshot /dev/vg_cyrus/lv_cyrus. We then mount the snapshot > > -- > No virus found in this outgoing message. > Checked by AVG. > Version: 7.5.432 / Virus Database: 268.15.7/569 - Release Date: 05/12/2006 > 03:00 > -- No virus found in this outgoing message. Checked by AVG. Version: 7.5.432 / Virus Database: 268.15.7/569 - Release Date: 05/12/2006 03:00 ---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
