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тАО02-10-2005 04:12 AM
тАО02-10-2005 04:12 AM
Duplicate lvol
We are planning to move 1TB of data in lvols of 2GB and we would like to be sure that we do it as fast as possible (we cannot use mirrors).
We are plannning to use dd with a block size of 4MB (one PE and multiple of 512b) and the raw lvol.
Is the raw device the best idea?
Thanks in advance.
Best regards
jose
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тАО02-10-2005 04:20 AM
тАО02-10-2005 04:20 AM
Re: Duplicate lvol
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тАО02-10-2005 04:24 AM
тАО02-10-2005 04:24 AM
Re: Duplicate lvol
Yes, always use the raw device. The 'cooked' (aka, blocked) device file will go through the buffer cache, something you do not want at all. Note that mirroring would very, very slow. When you mirror an lvol, the task is done one extent at a time and every possible step is taken to ensure that the data is read correctly and then written to the mirror correctly. And during each extent mirror, all attempts to change the extent are put in a queue and will not be honored until the extent has been verified correct.
Bill Hassell, sysadmin
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тАО02-10-2005 05:13 PM
тАО02-10-2005 05:13 PM
Re: Duplicate lvol
Thanks for the information.
We are using HP-UX 11i (11.11), do you know for that version which is the maximum physical io size?
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тАО02-10-2005 07:49 PM
тАО02-10-2005 07:49 PM
Re: Duplicate lvol
1MB is the Maximum Physical I/O size of most versions of HP-UX
regards
yogeeraj
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тАО02-10-2005 07:51 PM
тАО02-10-2005 07:51 PM
Re: Duplicate lvol
see also: http://docs.hp.com/en/B3921-90010/physical_io_buffers.5.html
regards
yogeeraj
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тАО02-10-2005 11:03 PM
тАО02-10-2005 11:03 PM
Re: Duplicate lvol
Thanks for the messages.
We called HP and we got the following:
"...we have a limitation of 256k in all cases except the case of accessing disk block device bypassing LVM layer where the limitation is 1Mb.
Note that if customer uses striping in LVM - then the limit is more severe - stripe size might be less than 256k..."
Best regards,
jose
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тАО02-10-2005 11:05 PM
тАО02-10-2005 11:05 PM
Re: Duplicate lvol
Thanks