[linux-lvm] copy lv from lv?
yue
ooolinux at 163.com
Fri Apr 1 02:46:26 UTC 2011
1.what i mean is that, when copy one lv, i would like use it's snapshot, not origin, because origin is always template. making a snapshot is very quick.
but if can take a thousand snapshots from one lv, same size as origin? while the snapshots are readable and writable?
thanks
2.nice -5 dd if=/dev/clones/from bs=64M iflag=direct |
dd of=/dev/scratch/to bs=64M oflag=direct
the pipe base on STDIN,STDOUT. i do not think STDIN,STDOUT have too mush cache
At 2011-03-31 08:27:52,"Stuart D. Gathman" <stuart at bmsi.com> wrote:
>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 at 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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