tlug: DAT/DLT/AIT tapes

[joem <joem@example.com>]

Andy Howell wrote:
> I would recommend staying as far away from 4mm drives as possible. I've
> had two break at work and 1 at home. No amount of cleaning etc would
> revive them. When I do use them, which is usually for taking stuff to
> clients, I always "tar tvf" to make sure whats onthere is readable. 
> Many times I have arrived on site only to find the tape was unreadable.
> I know they are not cheap, but 8mm Exabytes are very reliable...

This parallels my experience exactly.  I have 6 broken DAT drives in a
parts box now - the MTBF for these seems to be about 1 year. The failures
tend to be of two types: 
    1)  The drive mechanism gets bent due to a large force being
        applied to the DAT tape on insertion at an angle incompatible
        with the drive geometry  (someone forced it in cock-eyed)
    2)  The motor becomes too weak to pull the tape out properly -
        perhaps a belt problem or tensioning problem.

I've test-driven two DLT tape drive systems and compared them to one
DAT3.  Here are stats from my tests.  "C" mode is using the tape's compression
firmware.  "N" is without.  The speed of DLT drives on a PCI SCSI card
using gzip'd files is about twice as fast as DAT.  Also, the tape capacity
is 29Gb compared to 9 Gb.  

The big plus however is reliability. The DLT drives and cartridges are
more stable than the DAT systems, and it is impossible to put the DLT
cartridge into the drive incorrectly since the tape self-inserts after
setting a lock (this is important when considering the effects of
part-time night-operators). 

The only drawback of the DLT drives is the cost (about $6000).

Two other contenders in the large-volume tape backup realm are the Sony
AIT and the Exabyte Mammoth, both at a rated capacity of 25Gb (which
usually means about 20Gb in practice) and with a data transfer rate 40%
less than the DLT.  

The Sony and Exabyte use AME (Advanced Metal Evaporated) tape, which has
much less binder as compared to the MP (Metal Particle) tape that the DLT
drive requires.  The AME tape leaves less residue and has a higher
potential data storage capability, which means that it will probably
become more popular in the future.

Summary:  DAT is out, DLT is in, AIT is coming.


--------------------------------------------------------------------

DRIVE   tape  file   bus  mode  run-time   maximum vol    rate
        type  type               HHMMSS        Mb         Mb/min
                                
HP7000  fuji  gzip   pci  35C   06:02:04      29934       82.69   
DLT     hp    gzip   pci  35C   06:04:53      29646       81.22      
        hp    gzip   pci  35N   07:15:40      32982       75.65   
        fuji  gzip   isa  35C   07:45:09      18228       39.20 
        AVERAGE THRUPUT (35C mode)                        81.96

TTI2300 hp    gzip   pci  35C   05:43:37      29337       85.28       
DLT     fuji  gzip   pci  35C   05:49:56      29502       84.29
        fuji  gzip   pci  35N   05:39:57      29193       85.86
        hp    gzip   isa  35C   06:31:27      15745       40.27 
        fuji  ascii  pci  35C   07:05:07      38306       90.13
        fuji  ascii  pci  35N   06:01:53      32272       89.15 
        AVERAGE THRUPUT (35C mode)                        84.79

HPDAT24 fuji  gzip   pci  ---   03:36:23       9360       43.33
DAT3    fuji  ascii  pci  ---   04:25:46      23107       86.87

--------------------------------------------------------------------


Joe Marchak
joem@example.com


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