On Tue, 24 Jul 2001 Jerome Fine wrote:
I have acquired a Sony SMO S501 and some cartridges.
that the company I bought them from used them for backup for at least
5 years. While each side of the cartridge holds only 300 MBytes, at least
the total capacity (both sides) is almost equal to a CD. And although
they are a bit slow on the WRITE operation, the READ operations are
almost as fast as a hard disk drive.
If you get a chance, check out a later-generation MO drive. Seek times and
transfer rates are much quicker.
I don't know about retention, but I expect I will
be making a backup of the
long term files about every one or two years. Does anyone know how I
might test a magneto optical cartridge for long term degradation?
I assume a similar accelerated-aging regime to testing CD-R discs would work;
high temperature and humidity.
What you can do (and this applies to CD-R discs as well) is check the
block/bit error rate. After writing to a new disk, use the SCSI READ LONG
command to read the raw data from each sector (this consists of the sector
data and error correction info). For each sector, see whether there is a
correctable error. End up with a figure for the percentage of sectors with
correctable errors. Do the same thing in a few years time, and see whether
there is any difference. A more accurate variation would be to record how many
"bad" bits are in each correctable sector.
Depending on the drive, you may be able to get it to automatically log the
number of times it has to use error correction.
You could establish a proportion of the maximum possible correctable bit
errors, and reject a disk if its maximum goes over that. (E.g., if up to 80
bit errors in a sector are correctable, you might reject a disk which has a
maximum of 50.)
Before evaluating error rates, make sure the disk's surface is clean; if you
have been using a particular disk heavily for years in a polluted/dusty
environment, dirt on its surface will probably affect the error rate. You're
interested in the "real" error rate, not errors which go away after cleaning.
Also make sure your drive's lens is clean.
Also, if I can read the cartridge, does that indicate
it is as good as when
it was written or should it always be written again after 5 years just to be
You can probably leave data alone for much longer than 5 years. Various MO
media manufacturers quote media lifetimes of 30, 50 or 100 years. Of course
they probably all use different criteria to come up with a lifetime figure...
If anyone ever sees a Sony SMO S501 for $ US 20 or
less, please send it
to me and I will always appreciate and accept it and pay you for the drive
and shipping in the US and Canada. Shipping from Europe is still too
Pretty much any ISO standard 5.25" MO drive will work with the 600/650MB disks
that the SMO-S501 uses; you are not restricted to that particular drive.