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SubjectRe: Volume Managers in Linux
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In message <71nrq2$ub7$1@palladium.transmeta.com>, H. Peter Anvin writes:
+-----
| Followup to: <199811030011.TAA29771@hilfy.ece.cmu.edu>
| By author: "Brandon S. Allbery KF8NH" <allbery@kf8nh.apk.net>
| In newsgroup: linux.dev.kernel
| >
| > In message <19981102235619.B1797@quit.mediaways.net>, Florian Lohoff writes
| :
| > | On Mon, Nov 02, 1998 at 03:57:20PM -0600, Shawn Leas wrote:
| > | > provides a way to GRACEFULLY combine multiple physical volumes
| > | > into a virtual contiguous logical volume, and gives a STANDARD
| > | > interface to applying alocation policies and even RAID.
| > |
| > | Yep - And even this Ted thought of beeing integrated into the ext234
| > | filesystem
| >
| > Erk. Logical volume management doesn't belong in the filesystem; it's a
| > device-like layer, not a filesystem-like layer.
|
| Not necessarily. If you want the filesystem to handle devices being
| added or even removed, you need some integration into the filesystem.
| It may be, though, that some should go into the RAID driver layer.
+--->8

I think the filesystem layer needs to communicate more with the driver layer
to handle this, but it's not really up to the FS.

A reasonable API should allow any fs to be layered on top of an MD / LVM
layer (think of LVM as being a variant of striping); if the fs doesn't know
about md a default strategy could be used, but if it's md-aware then the fs
can request specific handling for things. If the md layer is sufficiently
flexible as to allow variable-sized logical extents (that is, fixed size
within a particular logical volume but variable between volumes, presumably
always a multiple of the physical extent size), one could (for example)
create an md volume and then let "md-aware ext3" designate the use of
logical extents the size of cylinder groups. And a log-structured
filesystem could request that log extents be allocated on a separate device
from file extents if possible.

--
brandon s. allbery [os/2][linux][solaris][japh] allbery@kf8nh.apk.net
system administrator [WAY too many hats] allbery@ece.cmu.edu
carnegie mellon / electrical and computer engineering KF8NH
Kiss my bits, Billy-boy.



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