SSD cache with regular partition, like BSD swapcache

SSD cache with regular partition, like BSD swapcache

[Mark Hills]

For some time I've been hoping to use SSD caching, but cannot reasonably 
accomodate the superblock and new partition format.

Hence, looking for a non-writeback SSD cache which can be transparently 
added and removed from the system.

Of course it's at the expense of losing the cache content each time the 
cache is attached -- but for many useful cases and workloads this is 
absolutely ok, eg. workstations (using suspend-RAM) or full-time servers.

Doesn't look like it's possible from the docs; has there been any work on 
this -- a different 'glue' or front end?

IIRC the first public announcement of bcache did something similar -- 
hooked into the system by re-routing the I/O requests to a specific disk.

Tho I did not test it, it looks like DragonFly BSD has what I'm looking 
for, as part of its "swapcache" feature -- looks very easy to set up:

  http://www.dragonflybsd.org/docs/howtos/swapcache/

Thanks

-- 
Mark

Re: SSD cache with regular partition, like BSD swapcache

[Adam Brenner]

> Hence, looking for a non-writeback SSD cache which can be transparently
> added and removed from the system.

Removing / Adding a caching device within Bcache can be done on a live
system, so long as a backing device is created before hand. This was
explained here:
http://comments.gmane.org/gmane.linux.kernel.bcache.devel/1886

> Doesn't look like it's possible from the docs; has there been any work on
> this -- a different 'glue' or front end?

Is this what you are looking for? https://github.com/g2p/blocks

This should keep any data on the backing device without the need to format.

Hope that helps,
-Adam

--
Adam Brenner
Computer Science, Undergraduate Student
Donald Bren School of Information and Computer Sciences

Research Computing Support
Office of Information Technology
http://www.oit.uci.edu/rcs/

University of California, Irvine
www.ics.uci.edu/~aebrenne/
aebrenne-sXc7qaQca9o@public.gmane.org


On Thu, Aug 15, 2013 at 2:11 PM, Mark Hills <mark-UrrBsZIrrsb10XsdtD+oqA@public.gmane.org> wrote:
> For some time I've been hoping to use SSD caching, but cannot reasonably
> accomodate the superblock and new partition format.
>
> Hence, looking for a non-writeback SSD cache which can be transparently
> added and removed from the system.
>
> Of course it's at the expense of losing the cache content each time the
> cache is attached -- but for many useful cases and workloads this is
> absolutely ok, eg. workstations (using suspend-RAM) or full-time servers.
>
> Doesn't look like it's possible from the docs; has there been any work on
> this -- a different 'glue' or front end?
>
> IIRC the first public announcement of bcache did something similar --
> hooked into the system by re-routing the I/O requests to a specific disk.
>
> Tho I did not test it, it looks like DragonFly BSD has what I'm looking
> for, as part of its "swapcache" feature -- looks very easy to set up:
>
>   http://www.dragonflybsd.org/docs/howtos/swapcache/
>
> Thanks
>
> --
> Mark
> --
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Re: SSD cache with regular partition, like BSD swapcache

[Mark Hills]

On Thu, 15 Aug 2013, Adam Brenner wrote:

> > Hence, looking for a non-writeback SSD cache which can be transparently
> > added and removed from the system.
> 
> Removing / Adding a caching device within Bcache can be done on a live
> system, so long as a backing device is created before hand. This was
> explained here:
> http://comments.gmane.org/gmane.linux.kernel.bcache.devel/1886

Sorry, maybe I should have been more clear. I meant adding without 
modifying the _backing_ device.

> > Doesn't look like it's possible from the docs; has there been any work on
> > this -- a different 'glue' or front end?
> 
> Is this what you are looking for? https://github.com/g2p/blocks
> 
> This should keep any data on the backing device without the need to format.

Not really, keeping the data on the partition is only part of the solution 
-- and this requires free space before the partiion, or LVM.

As I said, I don't wish to modify the backing device at all (even in-place 
for risk to data) or use a new partition format (also prevents mounting 
the filesystem on other systems, or boot disks)

And it's just not necessary anyway if using a non-persistent read cache.

The nature of swapcache's integration makes it easier and less disruptive 
to configure -- especially for people who don't already use an initrd.

It would make it easier to experiement with the caching in different 
scenarios.

Thanks

-- 
Mark