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From: Ivan Voras <ivoras@freebsd.org>
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Subject: Re: ZFS Recordsize tuning & transmission (bittorent daemon)
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On 05/19/10 10:27, Arnaud Houdelette wrote:
> Hi,
> 
> I'm using the transmission bittorent client on a single drive ZFS pool
> (name unsafe). Downloading is mostly OK.
> But moving a downloaded file to an other zpool (zraid, name tank) takes
> ages.

You will generally observe the same problem with any file system you can
use because torrent (and other similar p2p) downloads target random
chunks of data in the files.

In most other "less smart" file systems (e.g. UFS) you can preallocate
the space (not by using sparse files but by really writing zeroes or
random junk in the length of the total file size), which you can't in
ZFS (or technically, can but you won't benefit from it). You cannot
"escape" from this feature of ZFS no matter what you do (except by using
expensive hardware).