Re: [9fans] ata drive capabilities

[Joshua Wood <josh@utopian.net>]

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> i don't know.  if you lean that direction, then the only thing raid  
> gives
> you is reduced downtime.

On reflection, it seems I do lean that direction, and generally use  
raid mainly to dodge downtime. Our plan 9 systems (and `other' alike)  
mostly have redundant disks (when they must have them at all) -- but  
they have regular offsite backup also. I wonder if I'm being wasteful.

> i think of raid as reliable storage.  backups are for saving one's  
> bacon in
> the face of other disasters.  you know, sysadmin mistakes,  
> misconfiguration,
> code gone wild, building burns down,
>
meteorite! ;)

> (and if my experience with backups is any indiciation, it's best  
> not to
> rely on them.)
>
Probably another discussion, but I try to deal with this by testing  
the offsite backups (rdarena output) of the plan9 fileserver against  
a similar system that's designated the second-string fileserver. I  
haven't had to do it in production in a while, (raid narrowed the  
reasons I'd need to) so maybe I'm missing something and it would be  
less successful than in the testing.

> but this thinking is probablly specific to how i use raid.  i  
> imagine the
> exact answer on what raid gives you should be worked out based on
> the application.
>
I probably veer toward mere semantics, but I'd still define your use  
of raid to be uptime-protection. The list of exceptions you place  
under ``backups are for...'' is the same list, essentially, that  
motivates the offsite backups I mention -- the usual holes in the  
raid prophylactic. I see how Plan 9 facilities (esp. dump) ameliorate  
some of them: admin mistakes, for example. But it doesn't fireproof  
the system.

Or, put another way, you're not asserting you have no backup beyond  
that fileserver raid, are you? Because if so, I want to learn how I  
can skip that step, too.

--
Josh




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