Thus spake Scott Haneda <[EMAIL PROTECTED]>, circa 6/15/2004 10:38 PM:
> If my email server were to have a hard drive failure, I could lose a lot of
> email [...] since IMAP is so I/O intense on the server, I would need SCSI
> or at least SATA 10K drives [...] It also ups the burden on me to backup
> the email server all the time, which can be hard since so many mailboxes
> are "in use" all the time. With POP is is simple.
There's also the quota issue. With POP, each time someone checks their mail,
they have an empty mailbox (or nearly so, if they're using online access).
With IMAP, this places more of a burden on the user to purge or archive mail
on a regular basis. Everyone will want larger quotas, so you'll need more
storage available if you switch your users to IMAP. RAID is the way to go.
With RAID 0, two drives are "mirrored" so that you have a hot backup in case
of a mechanical drive failure. (If bad data is written, of course, it's
written to both drives.) There's no improvement in speed or size, just
reliability.
With RAID 1, two slower drives are "striped" into one faster drive. Because
data is spread across two drives, instead of being concentrated on one, and
reads and writes can occur simultaneously on the two drives, throughput is
improved. A drive failure, unfortunately, takes down BOTH drives! You can
mirror two RAID 1 sets into a RAID 10 set.
With RAID 5, you can have massive amounts of storage by combining 4+ drives
into a single array, IO is faster due to the data being striped, and
reliability is high due to distributed parity bits. This means if disk 4/5
fails, the array still functions, albeit slower. When you hot swap the
drive, it is rebuilt automatically, albeit slowly, and when it has been
rebuilt, everything returns to normal automatically. You only lose data is
two drives fail simultaneously. I suggest an array of at least 5 drives,
with a spare available in case of drive failure.
RAID 50 combines the benefits of 5 and 0; you actually have a pair of
arrays, one mirroring the other. It's far and away the best option if you
can afford it. You only lose data is two drives fail simultaneously on one
array and the SAME TWO fail simultaneously on the other array as well.
Backup is, of course, a huge concern with so much data. If you can't afford
a tape library, you could use a big FireWire drive like LaCie's Big Disk.
I'm using one to back up a terabyte array until I can afford to upgrade it.
peter
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