RAID device nomination (Feature request)

[Martin <m_btrfs@ml1.co.uk>]

Dear Devs,

I have a number of esata disk packs holding 4 physical disks each where
I wish to use the disk packs aggregated for 16TB and up to 64TB backups...

Can btrfs...?

1:

Mirror data such that there is a copy of data on each *disk pack* ?

Note that esata shows just the disks as individual physical disks, 4 per
disk pack. Can physical disks be grouped together to force the RAID data
to be mirrored across all the nominated groups?


2:

Similarly for a mix of different storage technologies such as
manufacturer or type (SSD/HDD), can the disks be grouped to ensure a
copy of the data is replicated across all the groups?

For example, I deliberately buy HDDs from different
batches/manufacturers to try to avoid common mode or similarly timed
failures. Can btrfs be guided to safely spread the RAID data across the
*different* hardware types/batches?


3:

Also, for different speeds of disks, can btrfs tune itself to balance
the read/writes accordingly?


4:

Further thought: For SSDs, is the "minimise heads movement" 'staircase'
code bypassed so as to speed up allocation for the "don't care"
addressing (near zero seek time) of SSDs?



And then again: Is 64TBytes of btrfs a good idea in the first place?!

(There's more than one physical set of backups but I'd rather not suffer
weeks to recover from one hiccup in the filesystem... Should I partition
btrfs down to smaller gulps, or does the structure of btrfs in effect
already do that?)

Thanks,
Martin