Where are superblocks stored?

Where are superblocks stored?

[Rishi Malik]

Hi All,

 

I'm investigating some compact flash failures we've had. We run XFS on
the CF. I've been getting a lot of I/O errors around logical block
543080. These are 512MB compact flash cards, and I think that block puts
it at about halfway through the CF. I know the I/O errors indicate an
error at a lower level then XFS. What I'm wondering, is if there's a
superblock stored there? Maybe we're hammering that area a lot, and
because of other problems with the card, we're getting these errors. 

 

I know that XFS stores its primary superblock at 0, but I haven't found
out where the secondary superblocks are stored. Any help is appreciated.

 

Rishi Malik

 

 

 

Rishi Malik::Firmware Engineer::Rishi.Malik@adic.com
<mailto:Rishi.Malik@adic.com> ::o720-249-5932::c303-396-3568 

 



[[HTML alternate version deleted]]

Re: Where are superblocks stored?

[Chris Wedgwood]

On Mon, Jul 31, 2006 at 09:23:27AM -0600, Rishi Malik wrote:

> I'm investigating some compact flash failures we've had. We run XFS
> on the CF.

Generally, a journalling filesystem is a very *bad* idea for
compactflash.

> I've been getting a lot of I/O errors around logical block
> 543080. These are 512MB compact flash cards, and I think that block
> puts it at about halfway through the CF.

Probably the journal, by default it ends up being about midway in the
volume.

> I know the I/O errors indicate an error at a lower level then
> XFS. What I'm wondering, is if there's a superblock stored there?

There are superblocks for each AG staring at block 0 (xfs_info or
xfs_db will show you how large he AGs are).

> Maybe we're hammering that area a lot, and because of other problems
> with the card, we're getting these errors.

You've killed your flash with journal updates is my guess.  Use a
different filesystem.

Re: Where are superblocks stored?

[KELEMEN Peter]

* Rishi Malik (rishi.malik@adic.com) [20060731 09:23]:

> I'm investigating some compact flash failures we've had. We run
> XFS on the CF. I've been getting a lot of I/O errors around
> logical block 543080. These are 512MB compact flash cards, and
> I think that block puts it at about halfway through the CF. I
> know the I/O errors indicate an error at a lower level then XFS.
> [...]

It's most likely the internal log, sitting in the middle of the
fs.  BTW your mail address is bouncing.

Peter

-- 
    .+'''+.         .+'''+.         .+'''+.         .+'''+.         .+''
 Kelemen Péter     /       \       /       \     Peter.Kelemen@cern.ch
.+'         `+...+'         `+...+'         `+...+'         `+...+'

Re: Where are superblocks stored?

[Nathan Scott]

On Mon, Jul 31, 2006 at 09:23:27AM -0600, Rishi Malik wrote:
> Hi All,
> 
> I'm investigating some compact flash failures we've had. We run XFS on
> the CF. I've been getting a lot of I/O errors around logical block
> 543080. These are 512MB compact flash cards, and I think that block puts
> it at about halfway through the CF. I know the I/O errors indicate an

That would be the journal.

> error at a lower level then XFS. What I'm wondering, is if there's a
> superblock stored there? Maybe we're hammering that area a lot, and
> because of other problems with the card, we're getting these errors. 
> 
> I know that XFS stores its primary superblock at 0, but I haven't found
> out where the secondary superblocks are stored. Any help is appreciated.

The secondary superblocks are very rarely touched (repair, and
growfs only IIRC), they will be unrelated to your problem here.

cheers.

-- 
Nathan

RE: Where are superblocks stored?

[Rishi Malik]

Peter, Chris, thanks for the replies! I'm aware of the problems with
journaling filesystems on CF. I didn't design the system though! :) 

We're using 4096 size blocks for XFS. I think the logical block size in
linux is 512b, not 100% sure though. 

Thanks for letting me know the journal is there. I think you're right
about that killing the flash. 

I appreciate the help,

Rishi Malik

-----Original Message-----
From: Chris Wedgwood [mailto:cw@f00f.org] 
Sent: Monday, July 31, 2006 1:44 PM
To: Rishi Malik
Cc: xfs@oss.sgi.com
Subject: Re: Where are superblocks stored?

On Mon, Jul 31, 2006 at 09:23:27AM -0600, Rishi Malik wrote:

> I'm investigating some compact flash failures we've had. We run XFS
> on the CF.

Generally, a journalling filesystem is a very *bad* idea for
compactflash.

> I've been getting a lot of I/O errors around logical block
> 543080. These are 512MB compact flash cards, and I think that block
> puts it at about halfway through the CF.

Probably the journal, by default it ends up being about midway in the
volume.

> I know the I/O errors indicate an error at a lower level then
> XFS. What I'm wondering, is if there's a superblock stored there?

There are superblocks for each AG staring at block 0 (xfs_info or
xfs_db will show you how large he AGs are).

> Maybe we're hammering that area a lot, and because of other problems
> with the card, we're getting these errors.

You've killed your flash with journal updates is my guess.  Use a
different filesystem.



-----Original Message-----
From: Peter Grandi [mailto:pg_xfs@xfs.for.sabi.co.UK] 
Sent: Monday, July 31, 2006 11:48 AM
To: Rishi Malik
Subject: Re: Where are superblocks stored?


> Hi All, I'm investigating some compact flash failures we've
> had. We run XFS on the CF. I've been getting a lot of I/O
> errors around logical block 543080. These are 512MB compact
> flash cards, [ ... ]

That is a [euphemism alert!] very creative combination, and
perhaps I would not wholeheartedly suggest its use.

As to the errors, does <logical block> mean 512B sectors, 1024B
blocks or 4096B blocks? (consider carefully the implications...)