On Sat, Aug 28, 2010 at 11:01 AM, Doug Hughes <d...@will.to> wrote:
> * in vxvm lets you do everything from raid-0 to raid-6. lvm doesn't do
> mirror.
I'll make a point of contention here. From the lvcreate man page:
-m, --mirrors Mirrors
Creates a mirrored logical volume with Mirrors
copies. For example, specifying "-m 1" would result in a mirror with
two-sides;
that is, a linear volume plus one copy.
Specifying the optional argument --nosync will cause the
creation of the mirror to skip the initial resynchronization. Any
data
written afterwards will be mirrored, but the original
contents will not be copied. This is useful for skipping a
potentially long
and resource intensive initial sync of an empty device.
The optional argument --mirrorlog specifies the type of
log to be used. The default is disk, which is persistent and
requires a
small amount of storage space, usually on a separate
device from the data being mirrored. Using core means the mirror is
regener-
ated by copying the data from the first device again
each time the device is activated, for example, after every reboot.
The optional argument --corelog is equivalent to --mirrorlog core.
Also, while LVM proper cannot do RAID beyond simple mirroring, LVM
operates on top of block devices - of any type. Most hardware (even
local disk these days on server-class hardware) does RAID/mirroring
for you, in hardware. If you don't have such hardware, then you can
use the Linux md facility to do this to your heart's content.
I will agree that native Linux LVM cannot do the online relayout with
ease that VxVM can do, and the ext3 filesystem is a toy compared with
VxFS. However, whenever RHEL6 shows up (and in RHEL5 in tech preview
today, I think), you'll have ext4 which is a leap forward in the right
direction.
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