=3D?ISO-8859-1?Q?Ari_Sovij=3DE4rvi?=3D writes:T
> =

> > on a current i386 system I have almost all filesystems (incl. /) on a=

> > RAIDframe (level 1). The RAID set is automatically configured.
> > I don't understand why the rc.d raidframeparity check is done so late=
:
> =

> I've been wondering the same thing, as Linux for example initiates the =
rebuild =

> right after the autoconfiguring arrays have been detected and assembled=
=2E
> =

> > Shouldn't parity be checked (and possibly be rewritten) before filesy=
stems
> > are checked and mounted?

In theory, yes, but if you have a huge array that might take hours to =

check, you probably don't want the unavailable for that long.  The =

time it takes to do the check is the time your data is "unprotected" =

against a component failure, so whether you want to be "live" during =

is the question... =


> AFAIK the parity check is transparent, so once you initate it, you can =
go on =

> checking the disk and making modifications to it. I took a look at your=
 patch
> , =

> and I'd leave the ") &" line as it was.

Note that if you are doing a fsck at the same time as doing a parity =

check that they will be fighting against each other, and the fsck =

will take much longer than normal to complete.  If we ever get a =

filesystem that doesn't require a long fsck, then we'd certainly want =

to move the parity check to make it occur as early as possible.
 =

> Running FSCK on a RAIDframe array before parity check seems to actually=
 corrupt =

> the array.

Ummmm... "no".  At least, it's not supposed to, is something I've =

never seen happen in all the testing I've done, and if it is =

happening, RAIDframe should be disabled completely until the problem =

is fixed.

> Here's what happened to me:
> =

> The machine crashed under heavy load (updating pkgsrc & compiling somet=
hing).
>  =

> When it came up again, FSCK found lots of problems that got fixed =

> (which raises another question, shouldn't soft depensies prevent this?)=
=2E
> After FSCK RAIDframe parity was rewritten. After I logged in, I immedia=
tely
> rebooted the machine and surprise, FSCK found a whole new set of troubl=
e.

One fsck doesn't always find all the problems.  If you have a really =

nasty crash, multiple "fsck -f"'s might be needed before fsck doesn't =

find any further errors.  Just because you did one fsck doesn't mean =

it fixed all the problem!  (I wouldn't go blaming RAIDframe if you =

just did a single fsck after a nasty crash.)

> I thought about this for a while and came up with a theory, that the co=
ntent =

> on the disk were different at the time of FSCK. Maybe some data got wri=
tten
> on one disk before the crash so that the actualy filesystem metadata di=
dn't =

> match any more. So when FSCK was checking the array, it fixed (or left
> unfixed) something that wasn't the same on both disks. And when RAIDfra=
me =

> rebuilt the array, neither of the disks had perfectly checked and fixed=
 =

> file system.

If the parity is not known to be correct, then in a redundant =

configuration RAIDframe will *never* use the parity bits to construct
data.  In a RAID 1 configuration, this means that the mirror will =

never be read -- only the master will be read.  Writes will continue =

to go to both.  Reads from the mirror will only occur once it is =

known that the data for that sector is consistent across both =

components.  =


> I let RAIDframe to finish rebuilding and rebooted again. This time FSCK=
 came =

> up =

> clean. I found some corrupted files in the lost+found, all from /usr/pk=
gsrc. =

> So, no precious data was lost and the situation was recovered by regett=
ing =

> pkgsrc, but this left me thinking maybe the parity rebuild should be in=
itiated =

> before FSCK.

It really depends on how paranoid you want to be, and/or whether or =

not you can afford to wait for the parity check to complete.  The =

fsck could be done at the same time the check is being done, but that =

really just slows both down...   =


Later...

Greg Oster