[mythtv-users] XFS: options when running mkfs.xfs

[Andrew Burgess]

>> AFAICS the allocsize= XFS mount parameter is designed to prevent 
>> exactly that.
>allocsize can be set to a value up to 1GiB (in power-of-two increments),
>so--in theory--this could limit the maximum number of fragments to 8 for
>that 8.5GB file (= 7.9GiB) (though in reality, the number is likely to
>be greater due to other data on the disk).  It definitely helps, but
>writing a single file to a file system at a time (as is possible with
>Storage Groups, even with multiple capture cards) helps more.

>Let me put it this way, when Myth starts writing a file at 8:00pm that
>will grow to an 8.5GB file by 9:00pm, the file system doesn't set aside
>8.5GB of contiguous space on the disk.

I think it sets aside 1GB at a time, assuming allocsize=1G

>If Myth starts writing a second
>recording file at 8:00pm or 8:30pm or whatever, it is likely to be
>interleaved with the other file that's being written concurrently.

As I read the manpage, it would be interleaved in 1GB chunks.

Anyway, time will tell. It'll be months before I fill my new
XFS array, hopefully someone else will post some numbers before
then.