On Feb 23, 2010, at 2:20 PM, Dan wrote:
For Data security at the cost of speed is RAID 5 across 3 disks.
There is a parity bit so that if one drive fails, you still can
recover the data by replacing the failed drive. Slower than RAID 0,
but your data is secure.
until the RAID card itself dies, and spazzes out on the master
blocks. The replacement card cannot then recover things, so you've
lost it all anyway.
Which brings you back to Len's first query. Iffa you do RAID you
gots to keep really good backups or risk loosing EVERYTHING. Big
datacenters use RAID with LOTS of HDs - so they have both
performance and data integrity. AND they also push their data off
to other arrays.
What Dan said. We run a smallish (only 3 terabytes) buncha storage
here, and have been using RAID forever.
Contrary to what Len said RAID5 is NOT designed for data security, it
is designed for minimal downtime (If a drive fails, you can throw in a
new one and not take the raid offline while the RAID rebuilds itself.)
Backups are your ONLY Data Security...we've experienced the very thing
Dan warns about: a RAID card goes bad and barfs all over the RAID 5.
Kablooey. We had to put in a new card and rebuild the RAID from tape,
a process that took about 32 hours at the time, and at that we lost a
fair chunk of data newer than three days old (RAID died mid-
incremental backup)
--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group
Institutions do not have opinions, merely customs
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