Subject: Re: DEV_B_SIZE
To: Steve Byan <>
From: Alfred Perlstein <>
List: tech-kern
Date: 01/31/2003 11:11:27
I hope I'm not mistaken here, but for FFS to work it needs the 512
byte ops to be atomic, making them not so, or possibly obliterate
surrounding blocks doesn't sound like a good idea at all.

Shouldn't you guys be asking Dr McKusick?

I can forward this question on to some of the fs people at Apple
as well.

* Steve Byan <> [030131 11:01] wrote:
> On Friday, January 31, 2003, at 01:55  PM, David Laight wrote:
> >>Really? fsck can recover from losing 4K bytes surrounding the last
> >>metadata block written?
> >
> >The only metadata that matter are the inodes and (for ffs) the
> >indirect blocks.  You do really want the latter to be single disk
> >blocks - many systems actually write them synchonously.
> What could be the effect of losing surrounding blocks on the (failed) 
> write of an indirect block? Can we guarantee that fsck can reconstruct 
> the filesystem, modulo some recently-created or deleted files, or is 
> there a possibility of losing the entire filesystem?
> >The inode is (probably) only 128 bytes, losing an inode block
> >will lose the other files.
> >
> >A journaling filesystem probably already has ways around this...
> I think journaling filesystems need to know the atomic block size in 
> order to structure their log in a fault-tolerant way; I'm hoping 
> someone on these lists can provide some details.
> Regards,
> -Steve
> --------
> Steve Byan <>
> Design Engineer
> Maxtor Corp.
> MS 1-3/E23
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-Alfred Perlstein []
'Instead of asking why a piece of software is using "1970s technology,"
 start asking why software is ignoring 30 years of accumulated wisdom.'