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Re: [linux-lvm] Disk crash on LVM



Coming a bit late to this thread...

On Sat, 19 Sep 2009, Fredrik Skog wrote:

Thanks guys for your input on the matter.
I lenghtened the power cables and bought a full lenght SATA cable. Now the disk is in the freezer and in progress with pvmove. 10% now. so far so good. The reason i decided for the pvmove instead of dd or dd_rescue was the fact that i tried a pvmove before, so the process was already started but it stopped working on 1%. Now with a frozen and working disk it continued from where it left off.

I have found that with sequential reads like this, adjusting the readahead of the device with something like 'blockdev --setra nnn' can dramatically shorten the time needed to read the whole device.

The default usually seems to be too low when reading sequentially. If you haven't already adjusted it, try adjusting it upwards. Values like 8192 or 16384 may help.

Good luck,
Peter.

I can tell you how it turned out later.

Thanks

/Fredrik



----- Original Message ----- From: "André Gillibert" <rcvxdg gmail com>
To: <linux-lvm redhat com>
Sent: Saturday, September 19, 2009 4:11 PM
Subject: Re: [linux-lvm] Disk crash on LVM


Ray Morris <support bettercgi com> wrote:
[...]
   Then dd from the old copy of the LV to the new:

dd if=/dev/org/$1 bs=64M iflag=direct |
dd of=/dev/copy/$1 bs=64M oflag=direct

   That piped dd is 2-3 times faster than the "obvious"
way to run dd.
[...]

The issue with dd is that if any read() fails, it skips the entry (64M) and doesn't write to the output, making the output file smaller than the input file.

with conv=sync,noerror, it's better, but, still loosing a whole 64M block at once is a bad thing.

That's why I think dd_rescue would be better.
<http://www.garloff.de/kurt/linux/ddrescue/>

If it still gets warm too fast, I've heard that storing the hard drive in a freezer 24 hours may make it work again.
<http://geeksaresexy.blogspot.com/2006/01/freeze-your-hard-drive-to-recover-data.html>

If it crashes when dd or dd_rescue fails, it's possible to continue copying later, from the point it failed.

--
André Gillibert



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read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

_______________________________________________
linux-lvm mailing list
linux-lvm redhat com
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/


--
Peter Keller                                     Tel.: +44 (0)1223 353033
Global Phasing Ltd.,                             Fax.: +44 (0)1223 366889
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