Marco Peereboom wrote:
[push the disk back in]
Stale metadata, disk will remain unused from now on.
check
[pull the other disk]
You lose. all data is gone (for all intents and purposes).
check
# ls -l
total 4
-rw-r--r-- 1 root wheel 9 May 13 12:00 testo
[everything okay until here]
Nope, this comes out of cache.
# rm testo
rm: testo: Input/output error
[I still guess this may happen]
Shall happen.
Yes. And no.
Maybe I wasn't all too clear? My expectation is not (yet) the automatic
recovery of the respective half mirror! Sure not! I don't expect
miracles. What I do expect, though, is a consistent, defined and
predictable state.
Please, try to view it from a different perspective. Nobody would
voluntary pull out disk A, plug it back after 20 seconds, expecting it
to recover the mirror, pull out disk B after another 10 seconds, and
plug it back after 20 seconds, and still expect a full mirror!
But, and that's a big 'but' for me: some fault might do exactly that, a
flimsy controller, a faulty power supply. And then I don't want I/O
errors, and neither a panic at reboot. My expectations are much lower,
but based on consistency:
0. Running sane raid
1. One drive goes offline
What I'd expect, personally, would basically be minimally:
A. Immediate info about a drive lost.
B. 2 half mirrors remaining that I can plug into another box, at least
to access the data on either.
C. No further attempt to use that drive that went offline any longer, at
least not until a reboot.
D. That means, I won't have I/O errors, but the system running happily
from the active drive,
E. And it means that a reboot will go through smoothly.
I am aware that this implies, that when the second drive goes offline as
well, that NO more drive is available (even if either came back!). As I
mentioned, I request consistency of data, not necessarily uptime. I want
to be abe to retrieve the data from the drive that went offline first,
and I want to be able to retrieve data from the drive that went offline
later. Personally, to me RAID is not failover, or availability, but
access to the data up to and until that moment when a drive goes offline.
And I want a clean reboot, irrespective of all ups and downs of the drives.
Please, correct me if I am wrong!
Uwe
