[Discuss] Backing up LVM partitions using snapshots

[Richard Pieri]

On 12/15/2011 8:25 AM, markw at mohawksoft.com wrote:
> The problem I have with tape is how poor its reliability is. When I worked
> at Sytron, a tape backup software company, the reality was (and still is)
> that tape is not 100% reliable, hell, not even 99% reliable. Tape backups

Neither are disks, nor disk and RAID controllers, nor the people who use 
them.  Allow me to remind you of the RAID controller that I had go 
stupid earlier this year.  It quietly scribbled all over the file 
system, wrecking some 7TB of data.  This is why we make backups.  They 
are the tools we use to recover from failures and mistakes and disasters.

> are designed as a solution that accepts that if you have enough coverage,
> you'll probably be safe. Tape always has a risk that data will be lost and
> if you have enough tapes, your data is surely safe on one of them.

How is this at all different from replication?  Answer: it isn't.  The 
only practical difference is the medium.

> That model is changing. The EMCs, NetAPPs and the like don't rely on tape.
> They rely on the sort of strategy I am describing. Duplicate reduction and
> replication, not "backup."

This is just another tape is dead marketing spiel used to sucker IT 
purchasers.  The promise of "lower costs" convinces them that storage 
frames and cloud storage is the way to go.  It's a trap.  A storage 
frame has finite capacity.  If you want to expand beyond that limit then 
you have to buy another frame or an expansion chassis.  Tape libraries 
are infinitely expandable: you buy more tapes.  Those tapes are going to 
cost an order of magnitude less than the cost a new frame.  Really. 
300TB of LTO-5 costs $10,000-$15,000; a 300TB raw capacity EMC Symmetrix 
starts around $200,000.

I'm not going to say you shouldn't buy disk-based backup systems.  I use 
them myself for some purposes.  They're a useful stage for enterprise 
backups.  They are not the be-all to data integrity.  Layers of 
protection is how you maintain the integrity of your data.  Reliance on 
any single technology or device is a mistake.

I'm not just saying that.  I'm saying that from my experiences at a big 
EMC shop (Thomson-Reuters) and a big TSM shop (MIT).

-- 
--Rich P.