why is raid-5 not recommended for installations with more than 100 accounts?

[schemers]

It all depends on the amount of traffic on your system, as well as the size of your mailboxes.
RAID5 has poor write performance, and when a message arrives there are a lot of writes.
At a minimum:
- the whole message gets written to disk
- its content/headers/attachments gets anaylzed and indexed, which is multiple writes
- rows are inserted/updated in MySQL, as well as data written to the MySQL transaction log
- Zimbra has its own application-level journal file for crash recovery
- there are other log files written to (log4j server-level logging)
If you aren't having any noticable performance issues, you should be ok.
In general though, we recommend against RAID5 because in our testing we have seen very bad performance under it, to the point where a moderately loaded system will slow down to a crawl with RAID5, but have plenty of headroom on RAID1+0.

[kollross]

I fully understand that portion but i saw the comment that said
"I have 496 accounts in my Zimbra 3.1.4 with RAID5, so I couldn't migrate to version 4.0.4 "
And i checking if something major in code had not changed between 3 and 4 in the upgrade that we specifically prevent me from upgrading, and or seeing a huge performance difference between 3 and 4.

[14319KevinH]

[quote user="kollross"]I fully understand that portion but i saw the comment that said
"I have 496 accounts in my Zimbra 3.1.4 with RAID5, so I couldn't migrate to version 4.0.4 "
And i checking if something major in code had not changed between 3 and 4 in the upgrade that we specifically prevent me from upgrading, and or seeing a huge performance difference between 3 and 4.[/QUOTE]
Not at all. We just added the warning to the docs in v4. There is no code changes to make things slower on RAID5. In fact for IMAP things will be faster. If your happy with your system performance on version 3 then you'll be just as happy on version 4.