bad bread

bad bread

[boricua]

running reiserfsck -B bbfile   /dev/hda4 is giving me following error

"bread: cannot read the block 16 [i/o error]

anyway aroound this?

Re: bad bread

[rvalles]

On Fri, May 05, 2006 at 06:28:01AM -0400, boricua wrote:
> running reiserfsck -B bbfile   /dev/hda4 is giving me following error
> 
> "bread: cannot read the block 16 [i/o error]
> 
> anyway aroound this?
> 
IO error means block-layer level failure, that is, physical failure.

In the event of physical HD failure, the procedure goes like this:

- get a bigger partition somewhere reachable (new hard disk, nfs,
  whatever)
- boot knoppix, use dd_rescue to dump as much as possible of faulty disk
  into a file on the bigger partition. Pad not recoverable zones with
  zeroes so that the pointers arent screwed up.
- run fsck on the image you created
- mount and recover.

Good luck.
-- 
- Do you study theories? - Oh yes! Theories are fun. - How do you use them? - When I must act, theories are too slow. To act, I must know.

Re: bad bread

[PFC]

> In the event of physical HD failure, the procedure goes like this:

	Get mail saying a HDD is dead. Replace harddisk, resynchronize RAID.
	Use Linux software RAID. Harddrives are cheaper that the time you'll lose  
trying to recover your data.
	I have reiserfs on RAID1 on my PC ; the kernel can distribute random  
reads to both disks, so it is faster and more responsive.

Re: bad bread

[Valdis.Kletnieks]

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On Sun, 07 May 2006 10:35:44 +0200, PFC said:
> 
> > In the event of physical HD failure, the procedure goes like this:
> 
> 	Get mail saying a HDD is dead. Replace harddisk, resynchronize RAID.
> 	Use Linux software RAID. Harddrives are cheaper that the time you'll lose  
> trying to recover your data.

Remember to take backups *anyhow*.  That way, if the RAID controller dumps
cow manure on all the sectors, you won't be saying "Oh, SH*T".

Also, note that there exist buggy RAID controllers, where if you are doing
mirroring to 2 disks, and they develop bad blocks at different locations,
you can trash the mirror by resynchronizing (basically, you swap out one of
the bad disks, re-sync, it progresses as far as the bad block on the source
for the mirror, and dies).


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Re: bad bread

[Sander]

Valdis.Kletnieks@vt.edu wrote (ao):
> On Sun, 07 May 2006 10:35:44 +0200, PFC said:
> > > In the event of physical HD failure, the procedure goes like this:
> > 
> > 	Get mail saying a HDD is dead. Replace harddisk, resynchronize RAID.
> > 	Use Linux software RAID. Harddrives are cheaper that the time you'll lose
> > trying to recover your data.
> 
> Remember to take backups *anyhow*. That way, if the RAID controller dumps
> cow manure on all the sectors, you won't be saying "Oh, SH*T".

Or user error (rm -rf, fdisk, dd, mkswap) or bad memory or fire or
broken new kernel or script kiddies or worms/viruses or ..

	With kind regards, Sander

-- 
Humilis IT Services and Solutions
http://www.humilis.net

Re: bad bread

[PFC]

> Remember to take backups *anyhow*.  That way, if the RAID controller  
> dumps cow manure on all the sectors, you won't be saying "Oh, SH*T".

	Linux software RAID doesn't need a controller ;)
	But yes, backups should be done anyways.

	IMHO, RAID is good, harddisks are less reliable than the linux kernel,  
the linux RAID layer, and reiserfs.

> Also, note that there exist buggy RAID controllers, where if you are  
> doing
> mirroring to 2 disks, and they develop bad blocks at different locations,
> you can trash the mirror by resynchronizing (basically, you swap out one  
> of
> the bad disks, re-sync, it progresses as far as the bad block on the  
> source
> for the mirror, and dies).

	Linux RAID has a special option for that : you can trigger a check, which  
will re-read the entire disks and, if a read error occurs, re-write the  
failing sector with good data from the other drives in the RAID. The drive  
with the bad sector will then remap it to another sector.

Re: bad bread

[Valdis.Kletnieks]

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On Tue, 09 May 2006 00:18:32 +0200, PFC said:

> 	Linux RAID has a special option for that : you can trigger a check, which  
> will re-read the entire disks and, if a read error occurs, re-write the  
> failing sector with good data from the other drives in the RAID. The drive  
> with the bad sector will then remap it to another sector.

If you have 2 mirrored disks, and are replacing one, you don't have a good
block to read it from.  The failure mode was a RAID controller that didn't
properly handle re-writing the bad block on the first disk, so when the
second disk got a bad block, you were screwed....


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