Re: [ANNOUNCE] bcachefs!

Denis Bychkov
2015-07-20T02:52:10Z

I don't think I found anything in the design description or anywhere
else explaining how tiering works and what data, when and why ends up
on the next tier. And how to control this. The old bcache has a pretty
advanced set of knobs allowing you to fine-tune this behavior
(read-ahead limit, sequential cutoff, congestion thresholds, etc.) If
I overlooked, please point me to the right direction.

On Sun, Jul 19, 2015 at 9:44 PM, Kent Overstreet
<kent.overstreet@gmail.com> wrote:
> And yes, format ask drives as -C and use --tier for the slower drives.
>
> -B means an externally managed device - bcache doesn't remap anything to it,
> it exposes a passthrough block device just so it can snoop on accesses to it
> and cache them. The functionality still exists in the bcache codebase, but
> has no meaning in bcachefs land
>
> On Jul 19, 2015 6:41 PM, kent.overstreet@gmail.com wrote:
>>
>> Probably broken because I haven't tested them recently. Once I've unpacked
>> my computers (in a few weeks) I'll debug it
>>
>> On Jul 19, 2015 6:11 PM, "Denis Bychkov" <manover@gmail.com> wrote:
>>>
>>> On Tue, Jul 14, 2015 at 4:11 AM, Kent Overstreet
>>> <kent.overstreet@gmail.com> wrote:
>>> > On Tue, Jul 14, 2015 at 09:05:39AM +0300, Vasiliy Tolstov wrote:
>>> >> Does it support discards?
>>> >
>>> >> Format command have one device, how provide tiering?
>>> >
>>> > --tier specifies the tier of the devices that come after it, where the
>>> > smaller
>>> > index is the faster tier.
>>> >
>>> > Only tiers 0 and 1 are supported for now, that will be increased
>>> > whenever
>>> > someone gets around to it.
>>> >
>>> > If /dev/sda is your fast device and /dev/sdb is your slow device, run
>>> >
>>> > # bcacheadm format -C /dev/sda --tier 1 /dev/sdb
>>> >
>>> > bcacheadm format --help gives you the full list of options.
>>>
>>> Ok, I am really confused right now. So, the format utility still
>>> allows -B (backing device). Is it just an artifact left over after
>>> block caching? Because I could not make it work. Any thread
>>> encountering the formatted backing device just hangs inside the
>>> kernel space until reboot. Is there something wrong with my setup or
>>> backing devices are just an illusion, a figment of kernel's
>>> imagination? And, if not, how do they relate to tiers?
>>> Could you give a simple example of a usual setup - one small and fast
>>> SSD and huge but slow RAID-6? Should I now format both partitions as
>>> -C and assign tier 1 to RAID-6?
>>>
>>> >
>>> >> 14 июля 2015 г. 3:58 пользователь "Kent Overstreet" <
>>> >> kent.overstreet@gmail.com> написал:
>>> >>
>>> >> > Short announcement, because I'm in the process of moving - but I
>>> >> > wanted to
>>> >> > get
>>> >> > this out there because the code is up and I think it's reasonably
>>> >> > stable
>>> >> > right
>>> >> > now.
>>> >> >
>>> >> > Bcachefs is a posix filesystem that I've been working towards for -
>>> >> > well,
>>> >> > quite
>>> >> > awhile now: it's intended as a competitor/replacement for
>>> >> > ext4/xfs/btrfs.
>>> >> >
>>> >> > Current features
>>> >> > - multiple devices
>>> >> > - replication
>>> >> > - tiering
>>> >> > - data checksumming and compression (zlib only; also the code
>>> >> > doesn't
>>> >> > work with
>>> >> > tiering yet)
>>> >> > - most of the normal posix fs features (no fallocate or quotas yet)
>>> >> >
>>> >> > Planned features:
>>> >> > - snapshots!
>>> >> > - erasure coding
>>> >> > - more
>>> >> >
>>> >> > There will be a longer announcement on LKML/linux-fs in the near
>>> >> > future
>>> >> > (after
>>> >> > I'm finished moving) - but I'd like to get it a bit more testing
>>> >> > from a
>>> >> > wider
>>> >> > audience first, if possible.
>>> >> >
>>> >> > You need the bcache-dev branch, and the new bcache tools - be
>>> >> > warned, this
>>> >> > code
>>> >> > is _not_ compatible with the upstream bcache on disk format:
>>> >> >
>>> >> > $ git clone -b bcache-dev
>>> >> > http://evilpiepirate.org/git/linux-bcache.git
>>> >> > $ git clone -b dev http://evilpiepirate.org/git/bcache-tools.git
>>> >> >
>>> >> > Then do the usual compiling...
>>> >> >
>>> >> > # bcacheadm format -C /dev/sda1
>>> >> > # mount /dev/sda1 /mnt
>>> >> >
>>> >> > The usual caveats apply - it might eat your data, the on disk format
>>> >> > has
>>> >> > _not_
>>> >> > been stabilized yet, etc. But it's been reasonably stable for me,
>>> >> > and
>>> >> > passes all
>>> >> > but 2-3 of the supported xfstests.
>>> >> >
>>> >> > Try it out and let me know how it goes!
>>> >> >
>>> >> > Also, programmers please check out the bcache guide - feedback is
>>> >> > appreciated:
>>> >> >
>>> >> > http://bcache.evilpiepirate.org/BcacheGuide/
>>> >> >
>>> >> > Thanks!
>>> >> > --
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>>> >> > linux-bcache" in
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>>>
>>>
>>>
>>> --
>>>
>>> Denis

--

Denis