On Sun, 17 Aug 2014 12:31:42 Duncan wrote:

OTOH, I tend to be rather more of an independent partition booster than 
many.  The biggest reason for that is the too many eggs in one basket 
problem.  Fully separate filesystems on separate partitions separate 
those data "eggs" into separate baskets, so if the metaphorical bottom 
drops out of one of those filesystem baskets, only the data eggs in that 
filesystem basket are lost, while the eggs in the separate filesystem 
baskets are still safe and sound, not affected at all. =:^)

The thing that troubles me about replacing a bunch of independent 
partitions and filesystems with a bunch of subvolumes on a single btrfs 
filesystem is thus just that, you've nicely divided that big basket into 
little subvolume compartments, but it's still one big basket, and if the 
bottom falls out, you potentially lose EVERYTHING in that filesystem 
basket!

I'll write the counter-point to this.

If you have several partitions for /, /var/log, and /home then losing any one 
of them will result in a system that's mostly unusable.  So for continuous 
service there doesn't seem to be a benefit in having multiple partitions.

When you have to restore a backup in adverse circumstances the restore time is 
important.  For example if you have 10*4TB disks and need RAID-1 redundancy 
(which you need on any BTRFS filesystem of note as I don't think RAID-5 and 
RAID-6 are trustworthy) then an advantage of 5*4TB RAID-1 filesystems over a 
20TB RAID-10 is that restore time will be a lot smaller.  But this isn't an 
issue for typical BTRFS users who are working with much smaller amounts of 
data, at this time I have to recommend ZFS over BTRFS for most systems that 
manage 20TB of data.

If you have a RAID-1 array of the biggest disks available (which is probably 
the biggest storage for >99% of BTRFS users) then you are looking at a restore 
time of maybe 4TB at 160MB/s == something less than 7 hours.  For a home 
network 7 hours delay in getting things going after a major failure is quite 
OK.

Finally failures of filesystems on different partitions won't be independent.  
If one filesystem on a disk becomes unusable due to drive firmware issues or 
other serious problems then other filesystems on the same physical disk are 
likely to suffer the same fate.

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