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

From: yue <ooolinux@163.com>
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] copy lv from lv?
Date: Fri, 1 Apr 2011 10:46:26 +0800 (CST)	[thread overview]
Message-ID: <1551167.2ce1.12f0ef45c4f.Coremail.ooolinux@163.com> (raw)
In-Reply-To: <alpine.LRH.2.00.1103302019060.412@bmsred.bmsi.com>

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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@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@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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