[rdiff-backup-users] Why Tape

[Greg Freemyer]

On Fri, 2003-09-26 at 18:50, Robert L. Knighten wrote:
> Greg Freemyer writes:
>  > 
>  > As a simple example HIPAA requires all logs be maintained for 7 years I
>  > think it is.
>  > 
>  > That sort of archival storage is definately best done on tape.
>  > 
> 
> In what way is this "best done on tape"?  
>
>  > I know my company stores 30 days of backups on ATA disks, but then
>  > archival backups are made to tape.
>  > 
> 
> Why?
> 
<snip>

Possibly I was being a little strong in my wording, but tape is
definately my preference for archival storage. 

Optical is also good, but not very dense currently and they don't have a
20 year real world history to prove themselves.  

Disk I avoid.

My reasons:

1) Initial cost:  Tape is still much cheaper than disk.  Even with
currnt ATA pricing, disk is over $1/GB.  Tape is closer to $0.50/GB.

If used, RAID controllers and extra disks drive up the initial cost much
further.

2) Maintenance cost: An individual tape like DLT or LTO is designed for
long term archival storage up to 20 years and require no "maintenance"
other than reasonable air-conditioning.  (20 years is long enough for
me.)

Disk drives are not even designed to store data in a powered down
configuration at all.  ie. If they are powered down, many drives will
start to lose data as quickly as 30 days.

Therefore disk drives have a monthly maintenance fee equivalent to the
electricity they burn.  (Possibly negligible, but often not.  Worth
doing the math.)

Even when powered on, disk drives under go "thermal decay".  Typically
that means that the data on the drive may start to disappear at some
point between 3 and 7 years from when it was written.

Since low-level format info is typically written only at the factory in
modern disks, that means individual disk drives have a typical life time
of 3 to 7 years from _manufacture_.

So, if you are doing archival disk storage, this means you need to
ensure you are using raid, and that your long term cost includes disk
replacement on a regular basis.

3) Shock resistance - Drop a tape and a disk drive from 3 feet.  Guess
which one will still have data on it.  Possibly not relavant.

4) Density (weakest argument) - Individual tape media can currently hold
500 GB uncompressed.  ATA Disks not far behind.  The real difference is
how much space does a 1000 tapes occupy vs. 1000 disks with their
associated electronics.

FYI: I recently went to HP World, they were definately saying that the
practice of recent backups on nearline storage with archival storage on
tape would be standard practice in the near future.

Greg
--
Greg Freemyer