On 10/18/13 07:31, Stuart Henderson wrote:
On 2013-10-18, Scott McEachern <[email protected]> wrote:
Circumstances change, and I might be able to redeploy those HDDs as a
RAID5 array. This, at least in theory, would allow the 18TB total to be
realized as 15TB as RAID5, gaining me 6TB.
even if softraid would rebuild raid5, I'd worry about additional
disk failures before/during rebuild for a volume of this sort of size..
(especially given that rebuilding is not automatic with softraid).
Follow-up:
Thanks to all that replied publicly and privately, the information was
most helpful.
RAID5 can't rebuild, so that's a show stopper right there.
However, now I understand why something I thought (at first) would be
important has been left unwritten: RAID5 has its own lengthy set of
problems. Like Stuart and others said, the potential for a secondary
HDD failure causing a catastrophic failure to the entire volume is far
greater than most people think. This link was given to me off-list, and
it's worth the 60 seconds it takes to read: (It's short and to the point.)
http://www.miracleas.com/BAARF/Why_RAID5_is_bad_news.pdf
My primary goal with RAID is data integrity, with total capacity taking
a back seat. As much as, in my case, 6TB seems like a rather large
loss, the potential for RAID5 failure to gain that 6TB isn't worth it.
Simply put, RAID1 (or even better, RAID10), is a superior course of
action for data integrity.
Assuming the numbers provided by CERN in that PDF are anywhere near
accurate, it seems to me that using RAID5 is not only counter to the
reason for RAID in the first place, but even reckless.
Thanks again folks for the advice. I'm sticking to RAID1.
--
Scott McEachern
https://www.blackstaff.ca
"Beware the Four Horsemen of the Information Apocalypse: terrorists, drug dealers,
kidnappers, and child pornographers. Seems like you can scare any public into allowing
the government to do anything with those four." -- Bruce Schneier
