Re: Blocket for more than 120 seconds

[Duncan <1i5t5.duncan@cox.net>]

Hans-Kristian Bakke posted on Sun, 15 Dec 2013 15:51:37 +0100 as
excerpted:

> # Regarding torrents and preallocation I have actually turned
> preallocation on specifically in rtorrent thinking that it did btrfs a
> favour like with ext4 (system.file_allocate.set = yes). It is easy to
> turn it off.
> Is the "ideal" solution for btrfs and torrenting (or any other random
> writes to large files) to use preallocation and NOCOW, or use no
> preallocation and NOCOW? I am thinking the first, although I still do
> not understand quite why preallocation is worse than no preallocation
> for btrfs with COW enabled (or is both just as bad?)

I'm not a dev only an admin who follows this list as I run btrfs too, and 
thus don't claim to be an expert on the above -- it's mostly echoing what 
I've seen here previously.

That said, preallocation with nocow is the choice I'd make here.

Meanwhile, a subpoint I didn't make explicit previously, tho it's a 
logical conclusion from the explanation, is that once the writing is 
finished and the file becomes like most media files effectively read-
only, no further writes, NOCOW is no longer important.  That is, you can 
(sequentially) copy the file somewhere else and not have to worry about 
it.  In fact, that's a reasonably good idea, since NOCOW turns off btrfs 
checksumming too, and presumably you're still interested in maintaining 
file integrity on the thing.

So what I'd do is setup a torrent download dir (or as I mentioned, a 
dedicated partition, since I like that sort of thing because it enforces 
size discipline on the stuff I've downloaded but not fully sorted thru... 
that's what I do with binary newsgroup downloading, which I've been doing 
on and off since well before bittorrent was around), set/mount it NOCOW/
nowdatacow, and use it as a temporary download "cache".  Then after a 
file is fully downloaded to "cache", I'd copy it off to a final 
destination in my normal media partition, ultimately removing my NOCOW 
copy.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman