[K12OSN] backend raid 1, raid 5 or none of the above?

john lists.john at gmail.com
Mon Aug 6 20:41:43 UTC 2007

Hi all,

I am waffling on a question that I hope you all will be able to help
me come to a resolution about. Should my backend file storage system
be software raid 1 or software raid 5 or non of these? OS is Linux of
course. My LTSP server resides on a different machine entirely.

I've already setup a RAID5 system with 3 active disks and one hotswap
by following a very good howto

My final setup uses /dev/md0 in a raid 1 config using 10 Gb to host
the OS and mbr
and /dev/md1 in a 1 tb raid 5 to host the file system which has been
partitioned with separate /home, /tmp , /usr, /var

However the more I think about it the more I am worried that I am
setting myself for pain in the future. I am thinking about dumping the
whole setup and going to  raid 1 for the following reasons:

1. My reading tells me that RAID 1 has a longer MTBF

2. RAID 1 offers redundancy similar to raid5 but also relative
simplicity because I can clone one of the disks and keep a copy around
in case of problems
3. RAID 1 offers comparable disk read times when compared to RAID 5

On the other hand:

RAID 5 offers large volume sizes which we are looking for
RAID 5 offers comparable disk read times when compared to RAID 1
RAID 5 doens't offer comparable MTBF rates as RAID as you factor in extra disk
RAID 5 may be more complex to administer or rebuild than a "simple" mirror

Perhaps if I am such a coward I should go with a single 500 gig disk,
and make a backup image with G4U or a hardware disk cloner (which we
have) and keep it on hand and do a incremental backup of student files
every night (which we intend to do anyway). That way, although
students might not have access to their resources for a day, at least
I would have a path to recovery that I already understand.

As a side note we have frequent power outages do to weather, isolation
etc, and I haven't looked into setting up linux to talk to UPS's. Is a
raided system more intolerant of having the plug pulled than a normal
Linux box running ext3?

waffle, waffle, waffle :-)

I hope folks will set me straight!



More information about the K12OSN mailing list