[Gllug] Reiserfs faster boot

[Simon Trimmer]

On Mon, 8 Oct 2001, Nick Hill wrote:
> as you can see, the 'compressed' random file is actually larger than the
> uncompressed random file by 34K!
>
> The file containing zeros has been compressed by a factor of 1000.
>
> AFAIK a hole in the filesystem is an area of unallocated space. It is
> irrelevant whether this space contains zeros, random data or whatever.
> The filesystem describes it as being free for use. If part of a file
> larger than the hole is allocated to the hole, the file becomes
> fragmented. Other parts of the file have to be written elsewhere.
> Consequently, reading the file becomes slower as the drive has to scan
> across the hard disk surface to find the rest of the file.

It's not worth getting into but it's not technically unallocated - you really
don't want to overcommit storage on filesystems, just because we can treat
some blocks as zeros doesn't mean they will always be zero :)

If you wanted to, in this case you could consider holes to be a performance
trick, disk is slow so it's a Good Thing if we can avoid blocking for a
stream we can generate internally.

FYI another use for holes is making multi gigabyte files on floppy disks :)

-Simon
Simon Trimmer <simon at urbanmyth.org>



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