[KLUG Members] RAID

[Adam Williams]

> We have a 1TB RAID5 array that lost two drives at the same time. 
> <sigh>

Yikes, very bad karma.

> It was on our critical file server. Needless to say panic followed and 
> schedules were delayed....
> We bought an identical unit and a different brand of drives just for 
> diveristy. We really wanted to now mirror two RAID5 arrays.

Thats RAID 51 (mirrored RAID 5).  Why not just RAID 50?

> The RAIDs are Promise Ultratrak SX8000s. Adaptec said we could use one of 
> thier SCSI RAID cards to mirror the RAID5s. However, now that I'm trying 
> to configure the RAID card for RAID1 it says there are no usable drives.
> However, it detects the devices on bootup at the proper size. 
> Adaptec now says I can't do this. I bit late.

I'd be surprised.  One needs a really high-end card for this.  Something
like a "IBM ServeRAID-4L" maybe. 

> I looked at Linux software RAID, but the man pages are littered with 
> words like BACKUP and MANY BUGS.

I've used md for years, never had a glitch.  My master DSA is on an md
mirrored box, so I must trust it....

> So this brings me down to running one RAID as the active drive and 
> mirroring the changes each night to a second identical RAID drive.
> Is there a program for this? Is there a recommend way to keep two drives 
> in sync? I thinking a cron job?

If your distro has LVM support this should be pretty easy.  Snapshot &
backup/restore to the other array.... but why not just use tape?  If it
isn't "hot" this is a pretty serious solution.