What a good two port stata raid 1 pci controller

Kent Borg kentborg at borg.org
Wed Apr 7 18:19:36 UTC 2010


jgarciaitlist at gmail.com wrote:
> What a good two port stata raid 1 pci controller supported with drivers under ubuntu?

Use Linux software raid. It has been very thoroughly debugged, is high
performance, is flexible, and is cheap.


Hardware raid can be dangerous: what happens if the raid card itself
goes bad? Where are you going to get a replacement? How long will it
take to get the replacement? What if the card dies two years from now,
will you even be able to find an exact replacement? And, if you can't
get an exact replacement, will your disks be in a format that can be
understood by a different hardware raid card?

Raid should be used to make your system more reliable. If you run Linux
software raid there is no raid card to fail, fewer things to go wring
means more reliable.


Raid is not magic, however. Disks can still fail, and given enough time,
they *will* fail, and raid can't save you from everything...


Six general warnings about raid:

1) When running raid 1, do not use exactly matched disks in a single
raid 1 pair. The two identical disks living identical lives might die in
quick succession when they both wear out. If instead you have disks from
different manufacturers, chances are one will be less well made than the
other and die first.

2) If a disk dies replace it /immediately!/ High priority! High priority!

3) If you can, replace your disks before they finally quit working.
Disks keep internal "smart" statistics on their health, you can look at
these with smartctl, I don't know whether Ubuntu currently watches these
for you and warns... (Anybody?) Try to get your disks staggered: for
example, if they are both getting old, replace the one that is worst off
according to smartctl, then maybe 9-months later, replace the other
disk; now you have a staggered pair.

4) The very day you replace one disk you will be seriously abusing your
other (old) disk: because every single bit on the old disk will need to
be copied to the new disk. Both deleted and in use bits--raid copies it
all. That abuse can cause your old working disk to die before the copy
is made. See warning #3: replace disks before they die! Software raid is
more flexible: If you are running a raid 1 pair and want to replace a
disk that is aging, with software raid, if you have the ports, you can
make it a three disk array while bringing up the new disk, and only once
the new disk is happy, remove the aging disk, possibly without even
rebooting. Inexpensive hardware raid probably doesn't have enough ports...

5) Over heating will kill your disks. smartctl can tell you the disk
temperature, keep them cool or they will fail early.

6) Raid is not a substitute for backups. If you accidentally delete a
ton of crucial data, raid 1 will dutifully delete it from both disks.


-kb

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