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Date: Mon, 11 Nov 2002 09:36:19 +0700
From: Eugene Grosbein <eugen@kuzbass.ru>
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To: Ian Dowse <iedowse@maths.tcd.ie>
Cc: FreeBSD-Stable <stable@FreeBSD.ORG>
Subject: Re: backups of SUPERBLOCK
References: <200211101250.aa33786@salmon.maths.tcd.ie>
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> The superblock location for cylinder group N in units of 512-byte
> sectors as fsck expects is:
> 
>         (fpg * N + cgoffset * (N & ~cgmask) + sblkno) * (fsize / 512)
> 
> Most recent filesystems don't use the per cylinder group superblock
> offset (cgmask is 0xffffffff) so this simplifies to:
> 
>         (fpg * N + sblkno) * (fsize / 512)
> 
> There are `ncg' cylinder groups, i.e. the values 0..(ncg - 1) are
> valid cylinder group numbers. For the above filesystem, fpg=32768,
> sblkno=16, fsize=1024, so that gives backup superblocks at 32,
> 65568, 131104, 196640 ... 1966112, 2031648.

Thank you very much!

> I guess dumpfs should have an option to print the list in the
> units that fsck expects.

It would be very useful. It is important for average administrator to have
simple way to get list of superblocks for existing filesystem. 

Eugene Grosbein

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