User guide
USING THE CORVUS MIRROR
This section is presented in
two
parts:
The first
part
consists
of
a general description
of
the
function
of
the
Mirror
and a general description
of
its software.
The second
part
consists
of
the specific application
of
Mirror
software
for
your particular operating system.
About images
With the
Mirror
you can make a video tape copy
of
an
entire disk
or
of
portions
of
a disk. This is called a 'backup.'
When the Corvus Mirror makes a
copy
of
data from the Corvus
drive, it makes redundant copies
of
each block
of
data.
This method
generally produces a few
soft
errors
during
the
backup process.
An
error may
occur
in one block
of
a multiple set
of
blocks.
A
soft
error is defined
as
an
error
in one or more
of
the redun-
dant copies
of
each disk sector (512 byte block), where there was
at
least one
good
block in the redundant copy.
If all
of
the redundant copies
of
a
block
are bad (have an incor-
rect
CRC) then a RETRY will be needed. Only during a retry will the
Mirror
firmware attempt to combine
the
multiple copies
of
a
block
to
produce a single good block.
Studies on the error rates
of
this
method
of
data storage have
not
been completed. However, it appears that errors are mainly a
function
of
the
quality
of
the video cassette tape. Certified VCR
tape is
not
presently available. But,
through
the use
of
redundancy
and
CRC error checking, the data recovery rates projected in the
use
of
the
Mirror
system meet
or
exceed those
of
competing tape
cartridge
systems and they far exceed the rates for diskettes.
WHEN
MAKING A BACKUp, YOUR VIDEO TAPE
RECORDER SHOULD BE SET
TO
ITS FASTEST SPEED.
THIS
IS
BETA I
FOR
BETA FORMAT AND
IT
IS
STANDARD PLAY (SP)
FOR
VHS FORMAT. SLOWER
SPEEDS
MAY
CAUSE THE
DATA
ERROR
RATE
TO
BE
GREATLY
INCREASED.
2-2