Recomendations for a Migration of a Cyrus mailStore with 70K users.

[Andrew Morgan]

On Wed, 16 Jun 2010, Nestor A Diaz wrote:

> Hello Cyrus People.
>
> I have been always a proud user of the cyrus email system, currently my
> larger cyrus installation is about 70K users, which have been working
> fine, however i need to make some adjustems to improve the resposiviness
> of the mailstore.
>
> At the begining i use only a default mailstore, on a ext3 formatted
> filesystem over a raid 10 / LVM, it works fine, however when it reaches
> the 32768 directories, (a limitation of ext3) i have to create another
> partition, and then another one, so i have currently 3 partitions in total.
>
> Having defined some criteria in order to group every user into a
> partition i will like some recomendations, taking in mind the current
> cyrus server tools which i currently don't know what are their current
> capabilities, my plan is to forget using cyrus partitions, and instead
> using LVM partitions and the propper links to the physical partitions
> from the logical one.
>
> So i currently have:
>
> partition-default : 30K users
> partition-alt1: 20K users
> partition-alt2 : 20K users.
>
> and then i will like to have just one partition:
>
> partition-default ext4 formatted with links to physical partitions based
> on the first letter [a-z] of the user.

Have you seen the hashimapspool option:

hashimapspool: 0
             If enabled, the partitions will also be hashed, in addition to the hashing done on con‐
             figuration directories.  This is recommended if one partition has a very bushy  mailbox
             tree.

This results in spool directories like 
"/var/spool/cyrus/mail/m/user/morgan".

Unless you have more than 32k users with the same first letter in their 
username, it should work well.

There is also a "fulldirhash" option, but I've never used it.

> I think LVM is a great advantage, and in some way aliviate the need for
> cyrus partitions, i it will lead me deal with the grow of a partition
> and data administration so easy without too much downtime.
>
> So, it means that accordingly to this stragegy which seems to be the
> most simple for me, what would be the best technical path to accomplish
> a good migration ? allowusermoves: yes option and renamemailbox is
> enoguth to do this task ? what if i want to do this online ? can i ? how
> ? is there any script that will help me do that ?

You can do online moves/renames.

> Any suggestions or migration histories are welcome !
>
> What about murder / perdition ? they make any sense in this configuration ?

Both Murder and Perdition would work to "scale out" to multiple servers. 
They do add complexity though, so there is always a trade-off.

 	Andy