Re: In-kernel units for block numbers, etc ...

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Thu, Nov 26, 2015 at 07:33:00PM +0000, David Holland wrote:
> On Thu, Nov 26, 2015 at 11:38:14PM +0700, Robert Elz wrote:
>  > (for 4K sector drives, cgd and lvm both give you 1/8 the space that
>  > you should have had on the device.)
> 
> Ewww....
> 
>  > ccd (especially if combining a 4k byte sector device with a 512 byte sector
>  > device) is simply a mess - perhaps almost a candidate for extermination.
>  > (Or maybe it can be resuscitated, who knows right now?)
> 
> I was already under the impression that ccd was a candidate for
> extermination even before this came up.
> 
> Does ccd serve any purpose that raidframe doesn't? (other than
> compatibility with existing deployments, which I don't think are many)

Yes.  CCD supports layouts that RAIDframe doesn't, ones that are more
efficient for many real-world workloads: with CCD, it's possible to
concatenate drives or stripe them with enormous, prime stripe units, so
that concurrent I/O streams are highly likely to parallelize across
multiple units.  There's no support for anything like that in RAIDframe.

Perhaps it's possible to do something like this using RAIDframe and LVM
in combination, but we can't ship full LVM support because many of the
utilities are GPL3, right?

Thor