Re: OS Level Backup Solution

[Matthew Caron <Matt.Caron () redlion net>]

On 12/19/2012 12:38 AM, Amit Bhardwaj wrote:
> I have checked internet and have found Bacula as possible solution but
> i am not sure if it takes OS level backup as i have mentioned above or
> not.

I do not believe so. I have used it in the past, but only for data, not 
the OS.

As a general case, it is exceedingly difficult to take a *good* backup 
of the OS while the OS is running, because it will often lock specific 
files or partitions such that the backup cannot have access to it. 
Further, you may lack specific partition metadata (RAID information, 
partition UUIDs, etc.) because that is only available at the raw disk 
level, not at the mounted filesystem level. As such, the only way to 
really ensure a good, full, bare metal backup is to boot from alternate 
media and clone the disk off. That way, you can be assured that nothing 
is touching the disk and messing things up.

Since VM servers emulate the underlying hardware, you can typically do 
this from the hypervisor. I believe it accomplishes this by 
checkpointing the state of the machine (which is a nearly instantaneous 
operation), then backing up the state at that point in time. Since it is 
outside the running guest OS, it can do this without issue.

The way I've solved this problem before is to have a triple RAID 1 setup 
(3 way mirror) and for backups we remove one of the disks from the pool, 
then image that disk. Since a single RAID item can be booted, we have a 
"seed" disk to which we can add other disks which then sync with the 
first. Once the backup is complete, the disk is added back to the pool, 
where it resyncs. This scheme worked great until the resync time took so 
long that it started bumping up against the next backup. After that, we 
just went to redundant machines and only backed up the data. Since the 
OS only takes an hour or so to install, and hardware is cheap, we'd just 
spin up another machine as need be. As an optimization of the above, if 
we had a pool of identical systems (say, like a webserver cluster), we 
would make a "master" disk and just image new ones from that as needed.

Hope that helps.
--
Matthew Caron, Software Build Engineer
Sixnet, a Red Lion business | www.sixnet.com
+1 (518) 877-5173 x138 office

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