[solved] Will copying a running system result in inconsistent backup?

rwd · 2009-04-10 20:49:35

If you copy a whole file system of a running system while data is being written to it will that result in an inconsistent snapshot? By inconsistent I mean that two files, or the first last part of a file are from different points in time? Does this differ per filesystem-type or backup method?

Last edited by rwd (2009-04-12 08:45:55)

brisbin33 · 2009-04-10 21:07:42

i think copying a running system is a bigger problem than that. there's a lot of files in /dev and /proc that you really don't want to copy/paste from one running system to another. if you want to move / do it form a live cd. if you're scripting a backup, then just backup /etc /usr /var and /home then restore those to the new system, you won't know the difference.

rwd · 2009-04-10 21:22:17

I remember with databases you can't generally just copy the database files of a running database and expect to restore it, /usr/ and /etc/ may contain static files, but some apps store things in sqlite databases in /home/ for example. My question was also a bit out of curiosity: do some filesystems have the ability to let you select an exact snapshot in time, just like a 'select' query in a rdms, (without having to access it from something like a livecd)?

Last edited by rwd (2009-04-10 21:23:54)

bender02 · 2009-04-11 06:29:46

rwd wrote:

do some filesystems have the ability to let you select an exact snapshot in time, just like a 'select' query in a rdms, (without having to access it from something like a livecd)?

nilfs

by the way you can copy the filesystem while it is running no problem. of course when a program has stored an inconsistent state of a file to the disk then it's its problem, but IMHO no reasonable (for instance journaling) filesystem will serve you an inconsistent state of a file, even when written to.

of course when taking backups you shouldn't backup /proc and /sys (dynamically created by the kernel) and /dev (dynamically created by udev and some static parts by the initscripts when booting).

Mektub · 2009-04-11 07:27:21

bender02 is right. I daily backup my running system to another partition.

I do boot from that partition mainly for testing purposes, like testing other kernels that could break my
running system.

mount /dev/sdb2 /backup
rsync -av --delete --delete-excluded --exclude="/proc/**" --exclude="/sys/**" 
                           --exclude="/dev/**" --exclude="/backup/"   /  /backup

Mektub

bernarcher · 2009-04-11 11:01:46

Mektub wrote:

bender02 is right. I daily backup my running system to another partition.
I do boot from that partition mainly for testing purposes, like testing other kernels that could break my
running system.
mount /dev/sdb2 /backup
rsync -av --delete --delete-excluded --exclude="/proc/**" --exclude="/sys/**" 
                           --exclude="/dev/**" --exclude="/backup/"   /  /backup
Mektub

I am just experimenting with this sort of rsync backup. Just one thing I do not readily understand, why do you exclude contents: "/proc**", etc. Would it not be more appropriate to exclude the whole directory, using instead:

mount /dev/sdb2 /backup
rsync -av --delete --delete-excluded --exclude="/proc/" --exclude="/sys/" 
                           --exclude="/dev/" --exclude="/backup/"   /  /backup

That way it doesn't even attempt to backup any of those folders.

Last edited by bernarcher (2009-04-11 11:02:22)

Mektub · 2009-04-11 23:02:02

bernacher,

I am just experimenting with this sort of rsync backup. Just one thing I do not readily understand, why do you exclude contents: "/proc**", etc. Would it not be more appropriate to exclude the whole directory, using instead:

"/proc/**" creates the empty /proc/ in the backup, and it is needed when booting.

"/proc/' will not create the directory.

Mektub

bernarcher · 2009-04-12 00:21:25

Mektub wrote:

"/proc/**" creates the empty /proc/ in the backup, and it is needed when booting.
"/proc/' will not create the directory.
Mektub

Ah, right! I did not think of that. Only noticed that rsync tried to copy the /proc, etc. contents as well which I definitely did not want.
Still studying man rsync. It appears somewhat overwhelming at first sight.

Thanks for the info.

Arch Linux

#1 2009-04-10 20:49:35

[solved] Will copying a running system result in inconsistent backup?

#2 2009-04-10 21:07:42

Re: [solved] Will copying a running system result in inconsistent backup?

#3 2009-04-10 21:22:17

Re: [solved] Will copying a running system result in inconsistent backup?

#4 2009-04-11 06:29:46

Re: [solved] Will copying a running system result in inconsistent backup?

#5 2009-04-11 07:27:21

Re: [solved] Will copying a running system result in inconsistent backup?

#6 2009-04-11 11:01:46

Re: [solved] Will copying a running system result in inconsistent backup?

#7 2009-04-11 23:02:02

Re: [solved] Will copying a running system result in inconsistent backup?

#8 2009-04-12 00:21:25

Re: [solved] Will copying a running system result in inconsistent backup?

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