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

["Nico Kadel-Garcia" <nkadel@xxxxxxxxx>]

Ligesh wrote:

> But in normal circumstances, what we do is, take an LVM snapshot,
> then mount it, and then tar/rsync the contents. That can be
> hazardous. Anyway, now that I have given it some consideration, it
> appears, you can indeed run e2fsck on the LVM snapshot, and get a
> consistent file system, albeit without the application buffers in the
> ram.
Yes, it can be hazardous. Most operating systems page out information, and 
only write it to disk when they get around to it. This means that you may 
have mixed in blocks of data in files that haven't been paged back out to 
disk yet, especially files that get lots of traffic such as databases. It's 
even worse for databases, because they play various software tricks to 
assure that certain operations go to completion lest the database be 
corrupted, and those techniques do *NOT* typically involve getting 
everything written to disk. So you may backup the db files in the midst of 
what is supposed to be an atomic operation.
Even operations that write to two files in sequence become risky, such as 
adding user accounts and getting the account in /etc/passwd and not in 
/etc/shadow, or not vice versa. Such risks are small in typical operations, 
but they're real. 

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