Subject: Re: parity check with root on raid
To: None <netbsd-help@netbsd.org>
From: =?ISO-8859-1?Q?Ari_Sovij=E4rvi?= <apz-list@2304.org>
List: netbsd-help
Date: 04/22/2005 18:44:37
> 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.)

Okay, maybe I was just a bit too paranoid about this. I've been experiencing 
rather annoying problems with RAIDframe the whole time I've been using 
2.0-series NetBSD. :-/

> 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.

In that case, why is RAIDframe still reading both in the mirror during 
FSCK even if the array is dirty? I keep my disks in mobile HDD racks which have 
their own activity LEDs, so I see how they're accessed. During boot-FSCK, I see 
both disks being active for 10 seconds, then first for 10 seconds, then the 
second for another 10 seconds. It goes on alternating between them until the 
FSCK is complete. But since parity is known being dirty, why are they both 
being accessed for reading?

Another question comes in mind; is there any way to change the behavior how the 
disks are read? For example, in FreeBSD's gmirror, the user can select between 
"lowest load", "preferred drive", "round-robin" and "split requests" modes.

-- 
Ari Sovijärvi
http://apz.fi/