cbs@cs.cmu.edu (Clauss Strauch) (06/26/91)
A while back I posted asking for practical experiences with 8mm vs
4mm tape drives. My specific questions were the comparative reliability of
the two drives and media, and what experiences people have had with the new
90m(2 GB capacity) DATs. I also asked for general comments as to what might
lead a sysadmin to prefer one media over another. The quick summary:
-- Reliability seems about the same.
-- Nobody who responded had actually tried the longer DATs.
-- Which you prefer seems a matter of taste and how well the medium
meets your needs (wrt capacity, access-time, etc). No surprise there.
The actual responses are included below.
-- Clauss Strauch
Engineering Design Research Center
Carnegie Mellon University
cbs@edrc.cmu.edu
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We've been using 90m sony tapes on an Exabyte device now for over
a year, I personally like them. We have a minor problem in that we have about
3.4 Gig's of disk, of which we are only using about 1.6. This does mean that
shortly we are going to have to re-evaluate our backup strategy, as a result
I have been looking at alternative methods, and I've found that the best around
is the 8mm tape for capacity and price.
> [ reliability ]
As part of the day to day backup strategy, a tape is not written to
more than 5 times before we scrap it, excepting of course the offsite archive.
we have had absolutly no problems with the reliabilty of the media. We do not
buy the data registered tapes though, we use standard sony P5-90 video cassetes
which are less than half the price (approx 6.50 as opposed to 16.50 sterling).
as far as the device is concerned we have had in the year that we've been
using it, only one problem: One day it chewed up a tape, from what I can glean
from the supplier it seems to have been a design error, that caused about one
in a thousand tapes to get chewed, they replaced the unit for an updated one
at no cost.
> [ general ]
I like our exabyte set up. In fact what I am likely to do when we change
the setup as we are moving the admin part of the company to an office next door
is to put all of the fileservers in one room, and run two networks, one for
admin and one for R&D and oput a bridge between them then run two tapes
simultaeneously (SP?)
::::::::::::::
We have an Introl 8mm, and it works just fine for backups. It is rather
slow in terms of tape movement, ejection, and loading. My only real
complaint is that the device driver that Introl wrote does not support
variable sized blocks (or blocks that are not factorable by 1024 bytes).
I have a user here who has almost 100Gigabytes of data on 8mm tapes I
cannot read. Both of these problems can be solved by using the newer
(high speed winding) 8mm drives, and rewriting the device driver.
I would find the 8mm tape drives much more useful if I could read/write
video format tapes (I know that it won't happen because of the limited
market, and that there are more differences between video 8mm and data
8mm than there are similarities).
In the same vein, I would like to be able to use a DAT drive for data,
audio, and still video (well I would actually like realtime video
playback, but DAT data rates do not allow it and lossy compression is
not acceptable). The problem with most (if not all) DAT drives on the
market today is the third level of error correction is built into the
drives with no way to bypass it.
I think that DAT still has a chance, but only if the laptop UNIX boxes
start using them as the primary data interchange (instead of 1.44Meg
floppies). I can just see a busy executive type on the road whose
500Meg hard disk died, trying to reload 100+ floppies.
::::::::::::::
I've worked with 4mm and 8mm in the past, and I found that the Archive 4mm drives
were excellent for restores when compared to the Exabyte 8m drives. With the
Archive drive, your guaranteed seek times (when using SCSI SEEK FILEMARK command) would
be 40sec., even if the data were somewhere toward the end of the tape. As I recall,
a colleauge said that with the Exabyte 8200, seek times could be much longer.
However, Exabyte has the newer 8500 drive, which has better seek times.
Also, the 8200 could take up to 2 min to initialize itself, and tape loading was slower
when compared to the Archive DAT.
::::::::::::::
We have a Gigatrend vanilla drive. We are upgrading to the hardware
compression model with a board swap very soon. Apparently they will also
bring out an EPROM upgrade to handle 90m tapes as well as both data formats
(DDS and D/DAT) in September.
> [ reliability ]
No problems with tapes at all. Probably 20 times is the most writes to a
tape so far. We use about 90% of a tape at present for full dumps.
> [ 2 GB tapes ]
I am interested in this too as we may upgrade our EPROMS in September.
> [ general ]
Have you looked at tape prices? Dat tapes are cheaper in Australia. Of course
per Megabyte they aren't but who completely fills up all their tapes? I have
not been using special tapes like my friends with 8mm drives have been. They
started out with cheap tapes and had problems ($15) and had to use the special
tapes ($36). We pay $22 for a dat tape. Most of my tapes are 20% full so I am
ahead on media costs!
::::::::::::::
> [ reliability ]
If you use good quality media (ie. not video grade 8mm tapes), both
formats seem to be quite reliable. We've been running 8mm for two years
and 4mm for almost a year now with no real problems.
> [ 2 GB tapes ]
The 90m tapes are a bit thinner-based, but shouldn't be that much of
a problem. Avoid data compression until a single compression scheme is
chosen; you don't want to be left out in the cold with unreadable tapes
twenty years from now.
> [ general ]
Not really. The technologies aren't very different. We use both and
have good luck with both. Now a couple vendors (ie. Contemporary
Cybernetics) we have had poor luck with, but that's not a technical problem.
::::::::::::::
> [ reliability ]
I found that DATs are pretty reliable. We have had weird problems
with our exabytes that don't happen on our DATs. At the same time,
Exabyte tapes "seem" to last longer. I ran a repeated read/write
test and the Exabyte (1400 cycles) lasted twice as long as the DAT
(700 cycles). This was on only 1 tape of each type so your mileage
may vary.
> [ 2 GB tapes ]
I would guess they work fine. I don't believe you need a special
drive to use 90m tapes. However, I haven't tried them in ours.
> [ general ]
I like the DATs, because they are smaller and better designed and the
drives are cheaper. DAT tapes are more expensive than exabytes in
the US, but the opposite here in Europe. There is a lot of
weirdness in the US because of the copyright stuff with the music
industry. The DAT drives, I would guess, are more reliable, but can't
tell. We have only had ours for a few months. One of our exabytes
broke after two years of writing one tape per day. The other exabyte
is new, so I can't say anything about it. My guess is that DAT will
only become popular over the long haul.
Be wary of 5GB tapes, because you can't write 5GB files with programs
that use 32bit indices. I think this will be a big problem in the
future that people have been ignoring for a long time.
Stick with the DDS standard (WangDAT, Archive DAT, Sony DAT). I
don't think GigaTape's Data/DAT standard is going anywhere.
We are going with DAT as our internal standard based on our
relatively limited experience. The drives just seem to be better
engineered. DAT is faster when you consider tape loading time
(Exabytes twiddle stuff a lot longer than DAT drives have to). You
can append data to existing DAT files while our Exabytes don't work
that way. Our DAT drives run on Sync SCSI, but our Exabytes don't.
We keep an Exabyte around for data interchange purposes.