Re: Sync over loop devices takes ages? [2.4.17]

Andrew Morton
2002-02-28T18:12:34Z

Pavel Machek wrote:
>
> Hi!
>
> I have a script (attached). At one point it tries to do sync... That
> sync take a long time, with disk mostly unused.

When doing (say) ext2-on-loop-on-ext2 you should always ensure
that the blocksize for the topmost filesystem is the same as
the one underneath. So probably you wanted `mkfs.ext2 -b 4096'.

If you have a 1k blocksize filesystem loop-mounted on a 4k blocksize
filesystem, every write of a 1k block requires a read of the underlying
4k block. Which is excrutiatingly slow.

Some readahead in the loop driver would help heaps.

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