support quality (Re: dump | restore fails: unknown tape headertype 1853384566)

[Karl Denninger]

Peter Schuller wrote:
>>> Yes, but it's for running a dump on a (L)ive FS and just spits out warnings
>>> to that effect and has no effect on solving the problem(s).
>>>       
>> Unless the filesystem is very busy, you will get your data backed up. 
>> If you have things like databases, I still would not trust 
>> snapshots.  
>>     
>
> Uh. If backuping up a live database from a snapshot is not
> trustworthy, either the snapshot facility is broken or the database is
> broken (i.e., not crash-safe to begin with).
>
> That said there are plenty of other reasos to use proper dump tools
> (data portability, confirming the ability to actually read all rows
> from a table, using a more often exercised code path and perhaps less
> likely to have edge case bugs, etc).
>   
The issue with backing up a database live comes in when the filesystem 
where the database and transaction log files are DIFFERS.  You can get 
into a pathological case in that instance.

If the transaction log and database itself are both on the same 
snapshotted entity (that is, the snapshot is pulled at the same instant 
in time for both) what you get BETTER be restorable or your database's 
transaction log facility doesn't really do what it promises to do!

-- 
--
Karl Denninger
karl at denninger.net