Stan Hoeppner stan@hardwarefreak.com wrote:
On 1/8/2012 2:15 PM, Sven Hartge wrote:
Wouldn't such a setup be the "Best of Both Worlds"? Having the main traffic going to local disks (being RDMs) and also being able to provide shared folders to every user who needs them without the need to move those users onto one server?
The only problems I can see at this time are:
- Some users will have much larger mailboxes than others. Each year ~1/4 of your student population rotates, so if you manually place existing mailboxes now based on current size you have no idea who the big users are in the next freshman class, or the next. So you may have to do manual re-balancing of mailboxes, maybe frequently.
The quota for students is 1GiB here. If I provide each of my 4 nodes with 500GiB of storage space, this gives me 2TiB now, which should be sufficient. If a nodes fills, I increase its storage space. Only if it fills too fast, I may have to rebalance users.
And I never wanted to place the users based on their current size. I knew this was not going to work because of the reasons you mentioned.
I just want to hash their username and use this as a function to distribute the users, keeping it simple and stupid.
- If you lose a Dovecot VM guest due to image file or other corruption, or some other rare cause, you can't restart that guest, but will have to build a new image from a template. This could cause either minor or significant downtime for ~1/4 of your mail users w/4 nodes. This is likely rare enough it's not worth consideration.
Yes, I know. But right now, if I lose my one and only mail storage servers, all users mailboxes will be offline, until I am either a) able to repair the server, b) move the disks to my identical backup system (or the backup system to the location of the failed one) or c) start the backup system and lose all mails not rsynced since the last rsync-run.
It is not easy designing a mail system without a SPoF which still performs under load.
For example, once a time I had a DRDB (active/passive( setup between the two storage systems. This would allow me to start my standby system without losing (nearly) any mail. But this was awful slow and sluggish.
- You will consume more SAN volumes and LUNs. Most arrays have a fixed number of each. May or may not be an issue.
Not really an issue here. The SAN is exclusive for the VMware cluster, so most LUNs are quite big (1TiB to 2TiB) but there are not many of them.
Grüße, Sven.
-- Sigmentation fault. Core dumped.