Detaching a cachine device

Detaching a cachine device

[Rolf Fokkens]

Hi,

I'm probably overlooking the obvious, but (as part of a test) I want to 
replace my caching device with a bigger one. So I think the first step 
should to detach the current caching device. I can find instructions 
about detaching a backing device, but that's not wat I want (the backing 
device holds the (slow) data, the important data). I can't figure out 
though how to detach a caching the device.

Any suggestions would be welcome,

Thanks,

Rolf

Re: Detaching a cachine device

[Gabriel de Perthuis]

> I'm probably overlooking the obvious, but (as part of a test) I want
> to replace my caching device with a bigger one. So I think the first
> step should to detach the current caching device. I can find
> instructions about detaching a backing device, but that's not wat I
> want (the backing device holds the (slow) data, the important data).
> I can't figure out though how to detach a caching the device.

Cache sets have an 'unregister' action: /sys/fs/bcache/<uuid>/unregister
The reference docs are in bcache.txt.
http://atlas.evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt?h=bcache-dev#n367

Re: Detaching a caching device

[Rolf Fokkens]

Yep, works indeed.

Dispite the alarming description :-)

Suggestion for alternative text:  "Detaches all caching devices and 
closes them; if any data is present in the caching devices it will ..."

On 09/15/2013 05:42 PM, Rolf Fokkens wrote:
> On 09/15/2013 05:20 PM, Gabriel de Perthuis wrote:
>> Cache sets have an 'unregister' action: 
>> /sys/fs/bcache/<uuid>/unregister The reference docs are in 
>> bcache.txt. 
>> http://atlas.evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt?h=bcache-dev#n367 
>
> I noteced that one, but it looks kind of scary to me:
> |"Detaches all backing devices and closes the cache devices; if dirty data is present it will disable writeback caching and wait for it to be flushed.|
> Sounds like one of these:
> - the /dev/cache* devices are gone; if so: that's definitely not what 
> I want.
> - or at least the the baching devices are detached; that also sounds 
> bad. I don't want to detacht the backing devices at all, I want to 
> detacht the caching device.
>
> The text is somewhat confusing to me. I'll give it a try, it's only a VM.

Re: bcache-status shows now output when caching device detached

[Rolf Fokkens]

When no caching devices are connected, bcache-status shows nothing. 
Although actually no caching happens, it's confusing.

On 09/15/2013 06:54 PM, Rolf Fokkens wrote:
> Yep, works indeed.
>
> Dispite the alarming description :-)
>
> Suggestion for alternative text:  "Detaches all caching devices and 
> closes them; if any data is present in the caching devices it will ..."
>
> On 09/15/2013 05:42 PM, Rolf Fokkens wrote:
>> On 09/15/2013 05:20 PM, Gabriel de Perthuis wrote:
>>> Cache sets have an 'unregister' action: 
>>> /sys/fs/bcache/<uuid>/unregister The reference docs are in 
>>> bcache.txt. 
>>> http://atlas.evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt?h=bcache-dev#n367 
>>
>>
>> I noteced that one, but it looks kind of scary to me:
>> |"Detaches all backing devices and closes the cache devices; if dirty 
>> data is present it will disable writeback caching and wait for it to 
>> be flushed.|
>> Sounds like one of these:
>> - the /dev/cache* devices are gone; if so: that's definitely not what 
>> I want.
>> - or at least the the baching devices are detached; that also sounds 
>> bad. I don't want to detacht the backing devices at all, I want to 
>> detacht the caching device.
>>
>> The text is somewhat confusing to me. I'll give it a try, it's only a 
>> VM.
>

Re: bcache-status shows now output when caching device detached

[Darrick J. Wong]

On Sun, Sep 15, 2013 at 07:34:46PM +0200, Rolf Fokkens wrote:
> When no caching devices are connected, bcache-status shows nothing.
> Although actually no caching happens, it's confusing.

Aha, I didn't quite understand what you were getting at until I broke one of my
cachesets.

Yes, it would be useful to have it report orphaned cache / backing devices,
since right now it only prints full sets in /sys/fs/bcache/$uuid/.

--D
> 
> On 09/15/2013 06:54 PM, Rolf Fokkens wrote:
> >Yep, works indeed.
> >
> >Dispite the alarming description :-)
> >
> >Suggestion for alternative text:  "Detaches all caching devices
> >and closes them; if any data is present in the caching devices it
> >will ..."
> >
> >On 09/15/2013 05:42 PM, Rolf Fokkens wrote:
> >>On 09/15/2013 05:20 PM, Gabriel de Perthuis wrote:
> >>>Cache sets have an 'unregister' action:
> >>>/sys/fs/bcache/<uuid>/unregister The reference docs are in
> >>>bcache.txt. http://atlas.evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt?h=bcache-dev#n367
> >>
> >>
> >>I noteced that one, but it looks kind of scary to me:
> >>|"Detaches all backing devices and closes the cache devices; if
> >>dirty data is present it will disable writeback caching and wait
> >>for it to be flushed.|
> >>Sounds like one of these:
> >>- the /dev/cache* devices are gone; if so: that's definitely not
> >>what I want.
> >>- or at least the the baching devices are detached; that also
> >>sounds bad. I don't want to detacht the backing devices at all,
> >>I want to detacht the caching device.
> >>
> >>The text is somewhat confusing to me. I'll give it a try, it's
> >>only a VM.
> >
>