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Re: [linux-lvm] copy lv from lv?



On Wed, 30 Mar 2011, Ray Morris wrote:

1..how to pipe two copy  together

This is what I use after some experimenting.  I've found
it's often far faster than the more obvious use of dd:

nice -5 dd if=/dev/clones/from bs=64M iflag=direct |
       dd of=/dev/scratch/to bs=64M oflag=direct

I use 64 MB extents. For smaller extents, a matching dd
block size might be good.

Thanks for that recipe.  It ought to be in lvm2 as an lvcopy utility
(dynamically determining extent size, etc).

2.i take lv as xen-guestOS's  disk. usually many  guestOS created
from one lv(called template), maybe many data is readonly, so  if  so
many lvs share readonly part ,and have its private data? COW save
disk space, and take less time. i do not think snapshot is sutable
for this case. thanks

As long as the origin is not often modified, having many snapshots
is efficient.  Each write to the origin will of course entail a write
to each snapshot.  (And as I discovered recently, if write barriers are
disabled or buggy at any hardware or software layer, a power failure during
heavy writes to the origin is particularly vulnerable to write reordering corrupting a snapshot. So make sure UPS is working before updating the
origin.)

--
	      Stuart D. Gathman <stuart bmsi com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.


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