Re: swapon vs savecore dilemma

From: Bakul Shah <bakul_at_bitblocks.com>
Date: Mon, 01 Sep 2003 20:31:42 -0700
> > Is fsck really that memory heavy so that it needs swap?
> 
> Yes, if you have a huge FS.
> 
> The problem is that the checking of the CG bitmaps during an fsck
> require that you have all the bitmaps in core

Hmm....
For a one TB FS with 8KB block size you need 2^(40-13) bits
to keep track of blocks.  That is 2^24 bytes or 16Mbytes.
That doesn't seem so bad (considering that you really should
have a lot more RAM if you are playing terrybytes of data).

> My suggestion (which has been my suggestion all along) is to add
> two date stamped CG bitmap bitmaps somewhere (my favorite place
> for this is to steal space at the front of inode 1, which is used
> only rarely, since people don't use the whiteout feature, and
> which can be made compatible with whiteouts, in any case).

This is the old stable storage idea.  You need a generation
number rather than a date stamp but the idea is the same.
Something needs to be done so that time to fsck depends on
the outstanding FS traffic at the time of the crash rather
than the size of the FS (especially when you are dealing with
multi terabytes of data).
Received on Mon Sep 01 2003 - 18:31:47 UTC

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