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We have dedicated CentOS machine running a customer management service, in a few days development will cease and we would like to take a complete backup of the hard-disks. The server has 2 500GB hard-disks using RAID1.

Now, I know that with dd (damn dangerous) we could take an exact mirror of the hard-disks (which is what we want), but I'm wondering if there less hardcore solutions that also offer incremental backups at a later point?

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add another harddrive as spare, remove one of the drives in the raid1 configuration, done. You now have a complete backup of the data, the raid will sync with the spare. Mind this is just a one-time snapshot, not a backup solution – Niko S P Feb 2 at 9:48
We also running cashier systems of the system so we do need the RAID system. However it's worth a consideration as a snapshot. – Ben Feb 2 at 10:07
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4 Answers

up vote 3 down vote accepted

Cloning/Mirroring solutions such as dd may not be able to provide incremental backup. If you want to have a backup at different points, you need to use a tool like rsync or a complete backup solution like backuppc.

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Love the idea of having a web front-end! Did you ever try it using backup over SSH? – Ben Feb 2 at 10:06
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@Ben: Backuppc has a web interface and it supports several ways of backup using rsync, rsyncd, tar, and others. You can rsync over SSH. – Khaled Feb 2 at 10:25
+1 for BackupPC & rsync! :) – Janne Pikkarainen Feb 2 at 10:29
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up vote 2 down vote

What is it that you're backing up? A relational database? Misc files?

How much downtime can you afford? (if you want low downtime then you really must start planing for unscheduled outages - meaning you need at least one other machine).

If it were me and there was a need to minimise downtime I'd break a disk out of the mirror (if there's a DBMS running on it then stop it first, break the mirror and restart to get a consistent snapshot). At most you're looknig at a few seconds of downtime. Then remount the filesystem from this disk somewhere else for backup. It can then be hot-joined back into the raid set.

There are ways to maintain the service when creating a consistent snapshot - but these are specific to the DBMS being used.

As for getting the data off the hard disk....for a DBMS, use the DBMS tools for generating a backup - a file image may not be portable across different versions of the DBMS. Every DBMS I've come across will allow you to run 2 instances on the same machine (as long as they are using different data files / network sockets).

Don't use dd or dump - in addition to no error checking, there can be portability issues with these too. cpio and tar have been around for a long time, tar can tricky when bitflips / corruption occurs. I've been using afio for some time - it allows individual files to be compressed (rather than tar compression where the output stream is compressed).

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up vote 1 down vote

You can use Clonezilla to make a image of a disk or partition compress it and upload it to a FTP or windows share. Read the documentation, because the software is very flexible.

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Thank you for your recommendation, but unfortunately we are looking for close to 100% uptime, so booting from CD is not an option – Ben Feb 2 at 10:04
To have a consistent backup you need either to stop the application, or to use a storage that allows snapshoting (like LVM) – Mircea Vutcovici Feb 2 at 11:56
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up vote 1 down vote

You're right. This type of question has been answered in several forms on this site. My recommendation for a point-in-time snapshot solution for Linux systems is the (free) HotCopy product from R1Soft. See the tips page for real life examples.

Basically, this is a kernel module and userspace tools that allow you to create copy-on-write snapshots of a partition on the fly. These snapshots do not persist across reboots, but can be handy for obtaining a clean copy of a dataset for shipping (rsync or otherwise) to another system/medium.

Also see: Clone/Mirror Live Linux (Debian) Server

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