Hooookay, well that was an interesting meeting! o_O



First, it appears that our head office is replacing their current 
arrangement with a big new SAN.

The concept of a SAN utterly baffles me. As far as I can tell, a "SAN" 
basically means that instead of connecting your HDs to the server that 
wants to use them, you connect them to a network instead, and then the 
server accesses it over the network. This has the following benefits:

* Tens of thousands of times more expensive than a direct connection.

* Hundreds of thousands of times reduced performance compared to a 
direct connection.

* Radically increased complexity compared to a direct connection.

* If the storage network fails, ALL servers fail, so you're adding a new 
single point of failure.

* All the servers now have to share the limited bandwidth available. One 
busy server can bring all the others to a crawl.

* Significantly more "enterprisey" than a direct connection.

Actually, wait... those are all disadvantages. Really, really /big/ 
disadvantages. Huh, OK. So why on Earth would any sane person embark on 
this course of action??

Oh, wait, I just found a real advantage: If you want to move a disk from 
one server to another, you just press a button, rather than having to 
physically move the device.

Oh, well, that /totally/ makes it worth it. And, uh, when will you 
*ever* need to perform this operation? I mean, seriously, I've been 
working at the UK site for almost 10 years now, and I've never once 
wanted to do this. And even if I did, if on one day in 10 years I have 
to shut both servers down to physically move a drive, I think I can 
probably live with that.

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. And with that many machines, perhaps the massive performance hit 
would be acceptable. But anywhere else? WTF?

Fortunately, this only affects HQ, so in a sense I don't have to care 
about this. Even so, it still baffles me.



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.

Jesus, this meeting just gets better, doesn't it?

First of all, speed. The LTO-3 tape system we currently use has a 
maximum transfer rate of 80 MB/sec. At that rate, 200 GB should 
theoretically take about 41 minutes (which agrees with my actual backup 
logs). But our Internet connection is a piffling 5 Mbit/sec. At that 
speed, 200 GB should theoretically take... 3 days + 17 hours.

And you want to do this /nightly/???

Second, what is the purpose of a backup? The purpose of having a "backup 
copy" of your data is so that if your working copy dies somehow, you can 
use the backup copy to get your data back.

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.

Third, having access only to the most recent backup is no good. There 
are scenarios where that would be perfectly OK, but in our line of 
business, we sometimes have to recover data from /months/ ago. Data that 
has been accidentally deleted. Data which got corrupted. Data which we 
thought we didn't need any more but actually we do. And so forth.

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. And, if we're going to continue our current policy of 
never deleting old backups, then the backup disk set must continue to 


that's far 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).

In all, this seems like an extremely bad idea.



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

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