FW: how to backup a cyrus server?

[Guus Leeuw jr.]

> -----Original Message-----
> From: Guus Leeuw jr. [mailto:Guus.Leeuw at guusleeuwit.com]
> 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 at lists.andrew.cmu.edu [mailto:info-cyrus-
> > bounces at lists.andrew.cmu.edu] 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 at lists.andrew.cmu.edu [mailto:info-cyrus-
> > >> bounces at lists.andrew.cmu.edu] 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
> 
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