[Dovecot] Maildir messages

[Wojciech Puchar]

>> mail accounts that must be very limited.
>
> There are many folks on this list who ran out of IOPS due to maildir at
> one time or another.  Nowhere near tens of thousands of accounts were
> not required.  To solve the problem, they either purchased more

did you actually monitored WHAT part of job generates I/O and how?

Can you post details. On just one simple

- how many mailboxes per disk head
- what filesystem used
- what OS
- how data is laid out.

> spindles, added RAID cache, or converted to mbox, or mdbox, depending on
> when they ran into the problem (mdbox is very young).
>
>> From my practice mail accounts are at least 1GB large, often 10GB. more
>> often than not other user data is on the same disk.
>
> Typical SMB setup it seems.

True. More - i always try to mix services. No separate "file servers", 
"mail servers", "whatever" servers but all on same. On large install 
divide by groups of people, not services.

This way i really cannot get to high IOPS.

>>
>> Mail I/O doesn't make that much part of I/O for me, still i found a bit
>> speedup by moving dovecot indexes to SSD if it exist.
>
> With only 50 users it's hard to saturate one disk with a mail workload.

True! That is my point.

With user taking few GBs of mail space (few tens not uncommon), as much or 
more "documents" or other data, you just will never have more than 50 of 
then on one disk.

More users=more disks, same (small) amount of I/O per disk head.

>
>> while disks get larger user data amount get larger too.
>>
>> Today tape backups are hardly used because it is plain uneconomic today.
>
> Tape is far more cost effective than a GbE MAN link to a hot site.

I really cannot imagine a scale of operation that would require gigabit 
link to do backups over rsync that only moves changes!

It would be like 10000 users on like 100 disks.

With that site i would think of tape.

Of course - no I/O problem to backup such 100 disk setup to tape.

> Again, those links are usually more costly than off site tape rotation
> services, and the backup window much larger.

my practice shows exactly opposite case.

If you would be right i would already use tapes or even pseudo-tapes== 
few cheapers hard drives connected over eSATA.

>
>> Adventages of pure Maildir format outweights everything else as you have
>> one file -> one mail.
>
> While that is maildir's greatest strength, it is also it's greatest
> weakness.

For my needs strength is great and weakness is small.

mdbox may help in your cases.


Seems like you do same ill service like 1000 (or more) mail accounts per 
hard disks.

My point was always "never delete old data, disks are cheap".