[CentOS] Replacing a hard drive
debian at herakles.homelinux.org
Wed Mar 14 22:46:24 UTC 2007
John R Pierce wrote:
> John Summerfield wrote:
>> John R Pierce wrote:
>>> dump 0f - /mnt/src | (cd /mnt/dst; restore rf - )
>> And presumably, fairly quickly. I've never used dump/restore, but if
>> it does the obvious and decides which blocks top copy, sorts the list
>> then copies, it should be quickest of all, regardless of the data
> dump/restore is an exact file by file copy of a filesystem, it
> replicates the directory entries quite exactly including all supported
> attributes.. I probably got in the habit of using it from Solaris,
> which has the rather similar ufsdump/ufsrestore.
I used to use, on OS/VS many years ago, a program called IEHDASDR. It
does a track-by-track dump of a disk, in track order, of those tracks
used by files and ignores tracks outside of allocated space. The only
track requiring special attention is cyl 0, track 0 which contains a
pointer to the VTOC (directory) which itself is a file.
My ordering the tracks, it all but eliminates seeking.
> another method is
> cd /source; tar clf - . | (cd /dest; tar xvf -)
That's what I said, more-or-less;-)
> but not all versions of tar have the -l (--one-file-system) option (gnu
> tar in CentOS does, however).
> oh yeah, dump will dump an unmounted filesytem too, so in fact, that
> could have been...
> mount /dev/hda1 /mnt/dst
> cd /mnt/dst
> dump 0f - /dev/hdb1 | restore rf -
That supports my suggestion that it might, like IEHDASDR, order the
block list so as to minimise seeking.
Archive programs such as tar are slow when there's a lot of data, but
perform relatively well when there's not a lot of files, and doesn't
copy deleted files. Tar causes lots of seeking.
dd is a straightforward sector-by-sector copy and is faster than tar
when the disk is relatively full of files, but it copies deleted files
and any other junk.
I think dump copies the smallest necessary volume of data, in the best
possible order. Its disadvantage is that it cannot change from own
filesystem to another.
There are other dump/restore programs for other filesystems.
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