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SubjectRe: atomicity
Hi Ted.

>>> With ext2fs you should never need a defragmenter

>> What does this mean? Is 22.4 % insignificant or should I be
>> worried?

>> /dev/md1: 2407/78624 files (22.4% non-contiguous), 185079/313260
>> blocks

> A high non-contiguous percentage doesn't necessary mean that your
> filesystem is highly fragmented. Files which are larger than the
> maximum number of data blocks available in a block group are
> guaranteed to be non-contiguous, by the very nature of the ext2
> filesystem.

> Hence, I was very hesitant when I included that metric in e2fsck,
> since it could be very easily misused and misunderstood. The
> problem is that doing a better metric is rather difficult.

> So for example, in the above example, there are 2407 files taking
> up 185 megabytes, for an average size of 77k a file. Given that
> there is usually a large number of small files (i.e., less than
> 10k), there is likely a goodly number of large files which are much
> more likely to overflow the confines of the block group and thus
> get counted as a "non-contiguous" file. But more simply, there's a
> big difference between a file which has the following allocation
> pattern:

> Blocks 10-8191, 8202-6000

Is that latter group valid?

> and ....

> Blocks 10-20, 30-56, 60, 64-66, 100-140, 142-143, 150-200, ....

> Both of the above two files are counted as a single
> "non-contiguous" file. But obviously, there's a very big difference
> as to the fragmentation of that particular file.

Perhaps a better metrics would be: Number of files containing multiple
partial block groups.

Best wishes from Riley.


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