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Re: SPARSE files considered harmful - please revert
On Sat, May 24, 2003 at 09:58:13AM +0200, Lapo Luchini wrote:
>Rolf Campbell wrote:
>>>3) What no one seems to be mentioning is that we are trying to emulate
>>>UNIX behavior here. If the above is an issue for Windows then it could
>>>also be an issue for UNIX.
>>And it is.
>e.g. from FreeBSD 4.8's "man mmap":
> WARNING! Extending a file with ftruncate(2), thus cre-
> ating a big hole, and then filling the hole by modify-
> ing a shared mmap() can lead to severe file fragmenta-
> tion. In order to avoid such fragmentation you should
> always pre-allocate the file's backing store by
> write()ing zero's into the newly extended area prior to
> modifying the area via your mmap(). The fragmentation
> problem is especially sensitive to MAP_NOSYNC pages,
> because pages may be flushed to disk in a totally ran-
> dom order.
And so, my point is proved.
Thanks. The feature stays.
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