Re: How to create bcachefs?

[Christopher James Halse Rogers <chris@cooperteam.net>]

On Thu, Aug 25, 2016 at 7:21 AM, marcin@mejor.pl wrote:
> W dniu 24.08.2016 o 08:52, Kent Overstreet pisze:
> [...]
> 
> Hi!
>> Hey, sorry for the long delay, been sick past several days.
> 
> I was afraid that I'm asking to easy question:) And I hope everything 
> is
> fine with you now!
> 
> 
>> The way arguments
>> were passed to bcache format was a holdover from old style 
>> make-bcache, \x7fand
>> didn't make much sense for bcachefs - -C was used for all devices, 
>> and \x7f--tier
>> specifies fast devices and slow devices.
>> 
>> I finally got around to redoing the option parsing so we don't need 
>> the \x7f-C
>> argument today - update your bcache tools, and the command you want 
>> is \x7fnow:
>> 
>> bcache format --tier 0 /dev/sde1 --tier 1 /dev/sdd1
>> 
>> (assuming sde1 is your fast device and sdd1 is your slow device).
> 
> Does it means that cache is unavailable and only tiering will be in 
> bcachefs?
> And... How to mount tiered FS? When I pass one device in mount I'm 
> getting:
>  bcache: bch_open_as_blockdevs() register_cache_set err insufficient 
> devices

Tiering gets you all the advantages of caching, plus you can (with some 
effort) have the combined filesystem size be the sum of the SSD + HDD 
capacities, rather than the capacity be determined solely by the 
capacity of the slow tier (this is not currently the case for bcachefs).

To mount a tiered FS you can either pass all the relevant devices to 
mount, like:
    mount -t bcache /dev/sda:/dev/sdb:/dev/sdc /mountpoint
(I haven't tested this recently) or ensure that all the relevant 
devices have been registered with bcache, like so:
    echo /dev/sda | sudo tee /sys/fs/bcache/register_quiet
    echo /dev/sdb | sudo tee /sys/fs/bcache/register_quiet
    echo /dev/sdc | sudo tee /sys/fs/bcache/register_quiet
    mount -t bcache /dev/sdb /mountpoint
(you can use any member of the set as the device to mount in this case).