On 8/3/2011 7:44, Invisible wrote:
> Perhaps if I worked at Google, managing 20,000 "servers" [which are really
> just commodity desktop PCs], having that many disks might be an issue.

 From what I've read, closer to half a million servers, all with the disk 
attached directly. :-)

> Second, they're replacing our tape backup system with a disk-based backup
> system. That's right, they're seriously talking about transferring over 200
> GB of data from our UK site to our USA headquarters, every night, via the
> Internet.

You generate 200G of incremental data a day? ow.

> This only works if the backup copy is more reliable than the working copy.
> If your working copy is on spinning disk, and you're stupid enough to put
> your backup copy on spinning disk as well... then it becomes equally likely
> that the /backup copy/ will die and you'll be left with just the working copy.

That's why you have two spinning disk backups that you alternate. Nothing 
wrong with spinning disk backup, especially if it's more reliable than the 
tape itself.

> So it's no good at all just mirroring what's on the server onto another
> server somewhere else. The /history/ must be kept. Now, there are various
> ways you might achieve that, but all of them unavoidably involve the set of
> backup disks being drastically larger than the total size of the working
> disks.

Not really. You don't actually change that much, I expect. Tapes don't have 
things like hard links and directories, but spinning disks do. Make a full 
backup, then an incremental once a day for a week, then a weekly 
incremental, etc, until you get up to monthly.

> something that's far less reliable.

I'm not sure how you know spinning disk is less reliable.

> And then there's the fact that you either need to keep all this disk
> spinning (i.e., ever increasing power and cabling demands), or only keep the
> recent backups spinning (i.e., managing powering off and powering on drives,
> which supposedly shortens their lifetime).

Once it fills up, you disconnect it and put in a new one, and you put the 
old on on the shelf.

> Still, what I do know? Apparently not a lot.

You know a lot. You should spend time writing this up, especially the 
bandwidth part, and send it to the people who would be able to evaluate this.

If nothing else, ask them what backup software they plan to use that will do 
incremental backups over a network and keep every old backup separately 
restorable.


-- 
Darren New, San Diego CA, USA (PST)
   How come I never get only one kudo?

Post a reply to this message