Re: number of global spares?

[Daniel Pittman <daniel@rimspace.net>]

"Guy" <bugzilla@watkins-home.com> writes:

[...]

>> I've been working on a RAID setup with dual RAID controllers and
>> three expansion boxes - 48 disks in all, including data, parity and
>> global spares.

[...]

>> They don't feel that the storage has to be blazing fast, and 100% uptime
>> isn't paramount, however they very much do not want to lose their data.
>> 
>> The filesystem will not be backed up - we simply don't have anything large
>> enough to back it up -to-, so if the some part of the storage solution
>> goes kerflooey, we're totally...  er...  out of luck, and they'll probably
>> be looking at me (the primary sysadmin on the storage configuration),
>> wondering why their data is gone.
>
> RAID5, 6 or 1 is not data backup!  It is hardware redundancy!!
> Data loss or corruption can still occur with a RAID solution.  RAID won't
> help if someone fat fingers a "rm" command.
> Corruption of the filesystem can also cause major data loss, without a
> failed disk.
>
> If the data was lost, what would it cost to re-create it?
> Enough to buy a backup system?

I absolutely agree with this.  When - and it is when, not if - the
content of this filesystem goes away, you will be rightly blamed for it.

Invest the few thousand dollars in a good high capacity tape drive and
pay someone to change the tapes.  This will be worth it when the system
finally does fail in some nasty, unpredictable way!

        Daniel