Re: Escaping Data Rot

[winston19842005 <bjjlyates@NOSPAMbellsouth.net>]

On 3/24/10 5:42 AM, in article
BbidnSe8TNkPQzTWnZ2dnUVZ_hidnZ2d@giganews.com, "Michael J. Mahon"
<mjmahon@aol.com> wrote:


> 
> I can't help but think that the practices of large IT departments are
> strongly shaped by tradition (to put it politely).  It seems to me that
> most high-availability database systems would be best backed up using
> a "floating triple-mirror" scheme, in which the system is never off-line
> and the backups are all onto (other) hard disks on off-site mirrored
> systems.  A journaled database and file system mesh beautifully with
> this approach.

At our hospital, we have two AS/400 systems, named HIS (Hospital Information
System) and HERS (perhaps Hospital Emergency Recovery System?).

We use journaling, backup the journals to tape every 3 hours (except not at
03:00 am).
We also use mirroring - whereby data is continuously copied from HIS to
HERS. At midnight, the link is broken, and we backup HERS to tape. Takes
about 3 hours. Then mirroring is restarted and it catches up. Of course the
disks are RAID, so there is even further redundancy.

So, just what you said, except HERS is located on-site in a different area
of the hospital.

> 
> The enterprise server backup problem is also functionally quite a bit
> different from the file archive backup problem.  Backups are generally
> used for two things:  to recover files lost to "operator error", and
> to restore a system database to a known-good point after a severe
> software or hardware failure, or for hardware upgrade.
> 
> The inherent "browsability" of a hard disk backup makes it very well
> suited to the recovery of particular files or groups of files, and to
> periodic "syncing" of file groups, which is a good match to the way
> individual users maintain their files.
> 
> I'm sure tapes can be used in this way, but this is not the typical
> "backup" scenario.  Certainly data cannot easily be updated in place.

Tapes were always too slow, and still are. Tapes in our case are used in
case of catastrophic events. They are rotated off-site and onsite are stored
in a vault in the basement.