Re: [Xen-users] Re: Mounting domU filesystem on Dom0. (xm mount)

["Fajar A. Nugraha" <fajar@xxxxxxxxxxxxx>]

Ligesh wrote:
> On Wed, Mar 14, 2007 at 02:23:40PM +0200, Siim Vahtre wrote:
>   
>> To get "really" consistent backup, the backup software must cooperate with 
>> the application, which can be quite complicated. But if the application is 
>> written well, it should be able to handle poweroffs, at least as far as 
>> not completely destroying your data.
>>
>> LVM is far from perfect, but I wouldn't say it is "terrible terrible" for 
>> your task.
>>     
>
>  With LVM, you get filesystem (kernel) level corruption. With nfs, you get 
> application level corruption. The first is obviously graver. 
I have to disagree.

When you restore something backed up from LVM snapshot, it is as if the
system was powered off at the time of the snapshot. As Siim mentioned,
some applications (e.g : Oracle or MySQL with correct settings) can
handle that nicely and provides a consistent, recovered, usable data.

Nfs backups, on the other hand, has no way guaranting consistent data.
An extreme example, think of a 100-GB MySQL Innodb datafile. If you copy
that file (via nfs or whatever) when MySQL server is running, the first
part and last part will most likely come from different points in time.
Good luck recovering that.

NFS backups SHOULD work out nicely for files that remains unchanged
during backup period (web pages, binaries, etc.).

Regards,

Fajar

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