At Sun, 21 Jun 2009 19:58:41 +0300 CentOS mailing list centos@centos.org wrote:
Without snapshots there is some risk to get inconsistent set of files when you make a backup of live file system. In general this is a problem but I'm not sure about your case. Actually there is another solution to this problem shutdown the system and take the backup using bootable CD/DVD (or booting from another OS installation).
You should unmount a file system before backing up with dd. You can also take a look at Clonezilla which is an open-source image-backup software.
The OP has no physical access to the machine, so unmounting the root file system is not possible. This pretty much rules out dd. dump and rsync WILL work just fine. Yes, the second disk won't be an exact mirror -- short of creating a software RAID 1 (mirroring) set it is not going to be possible to do that. I outlined (in another message) a reasonable procedure to create an up-to-date (within 24 hours) backup disk that will generally be an acceptable replacement system disk should the original disk die.
The 'inconsistenies' caused by a backup of a live file system are generally small are are not going to be fatal using proper backup tools (like dump, tar, cpio, and rsync). Mostly you will lose the last 24 hours worth of log files and stuff like that (assuming a once-a-day use of rsync). Nothing critical to the operation of the system.
2009/6/21 Rafał Radecki radecki.rafal@gmail.com
I think about using dd instead of dump? Is this an acceptable idea?
2009/6/21 Robert Heller heller@deepsoft.com
At Sun, 21 Jun 2009 11:49:09 +0200 CentOS mailing list centos@centos.org
wrote:
Hi all. I'm currently having a following problem: I have only ssh
connection
to a CentOS 5.2 system, there are two harddiscs on it. One stores the
system
(/ filesystem) and the other should be used to help restore the system
in
case of first disks' failure. I thought that maybe dump would be a good utility to make it. But in only works on read-only filesystems. In one
Dump works just fine on a read-write file system. There is the pretty much standard limitation (that applies to *all* backup methods) that when backing up an 'active' file system: there will always be files that will miss the backup because they were being written during the backup process.
article I've read that making a snapshot of the / filesystem (then it wouldbe read-only) and backing it could help. But aren't snapshots
limited
to logical volumes (LVM)? My friend told me to use rsync to back up the entire / filesystem to the second disk and then in case o failure the
system
from the copy should boot ok.
Could anyone provide any suggestions? I don't have physical contact with
the
machine so for example RAID 1 isn't a possible option/
Any help will be very kindly appreciated.
Make an initial dump to get the base system copied, then set up a cron job to sync the disks once a day (or more frequently) with rsync.
With regards, R.
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