The MDFS has a pretty impressive hardware specification. You can find out more about its hardware by clicking here.
The MDFS (Modular Disc File Server) was SJ's crowning achievement. Using a single Z80 processor,
it is a fully multi-tasking servers with both serial and parallel printer spooling and a
heirachical filing system.
It comes as a main box and a load of connectors, into which you could plug up to four double
density floppy drives, SCSI discs and a tape drives.
Server version 1.10 supported up to 8 partitions of 35Mb each - individual SCSI discs could have one or more partitions on them. Version 2.00 increased the partition size to 59Mb. The limit in the disc format is 64Mb, but it was kept to 59 to ensure that two partitions would fit on a 120Mb backup tape.
The MDFS was faster than Level 4 when it came out, and even now at small transactions the MDFS
is faster. Level 4 beats it for large data transfer, but it's surprising how much average usage
consists of small transactions where response time is more important than data transfer rate.
Many MDFS's now have a single drive of around 500Mb, with 8 59MB partitions. People would love
more disc space but it's just not pratical. All the tape drives are dying, they're expensive to
repair and you can't buy the tapes anymore anyway.
Workarounds vary from backing up using magneto-optical SCSI discs using raw partition copy in
utility mode through to backing up to an RiscOS machine over the network. Despite the backup
problems and disc space limit, people persevere with the MDFS because it is very reliable.
The MDFS supports the standard *commands, and adds a few of its own:
*ACCESS
Expanded to have 'P'rivate items. Also may report "/spl"
or "/prt" for items awaiting printing.
*ACCOUNT <userID> [<main account>] [(<aux. account>)]
Changes the main and/or auxillary account for the
user specified. User IDs may be wildcarded.
*BALANCE [<account>]
Report the balance of the specified account, or the
current account if nothing specified.
NOTE: This has changed since v2.00 of the MDFS
code. The syntax is now:
*BALANCE <account> <discname>
*DEFACCESS
Similar to *ACCESS; sets the default access
parameters. If you specify no directory, it will be
applied to the CSD.
This is useful for, say, a SYST directory where you
can set everything to be automatically made Private.
*DISABLE [SAVES | LIBRARY]
DISABLE on its own prevents the use of a wildcarded
deletion.
DISABLE SAVES prevents a file of less than 16 bytes
being saved.
DISABLE LIBRARY reduces the library searching to a
level equivalent to Acorn servers (ie: library is
only searched upon *RUN or *commands).
*DISCS
List the discs currently attached to the server.
*ENABLE [SAVES | LIBRARY]
Undoes the effects of *DISABLE.
*FLUSH
Flush any print entries from the user from the print
queue. This is useful if a program outputs too much,
or if ^B is accidently pressed.
*PRINTOUT <filename>
Causes the specified file to be printed to the currently
selected logical printer.
*REROUTE <print job name> <logical printer name>
Will reroute a printout in the print queue to another
printer. Can be rerouted to a�special printer "HOLD",
which holds the printout in the queue awaiting further
instructions.
And commands only available to supervisors:
*CREDIT <account number> <amount>
Add the specified amount to the balance of the
account given. Amounts are in units of 1K.
Maximum possible balance is 65535K, and setting
all balances to this value effectively disables
the accounting system.
The credit details the amount of space the user
has available, and NOT the space already taken.
NOTE: This has changed since v2.00 of the MDFS
code. The syntax is now:
*CREDIT <account> <amount> <discname>
*DEBIT <account number> <amount>
Performs the reverse of *CREDIT. If the
supervisor removes all credit, the account is
bankrupt and user cannot save anything.
NOTE: This has changed since v2.00 of the MDFS
code. The syntax is now:
*DEBIT <account> <amount> <discname>
*DESTROY <specifier> <disc name>
Used to destroy corrupted directories by turning
them into a file.
WARNING: Can be applied to root, with the
obvious consequences.
If you receive system messages such as...
Wrong number of files in dir. on drive 0
in WORK
And attempts to write to disc are replied with
"Disc Read Only", use this command to zap the
offending directory. You will lose the
directory and anything within.
*FINISH
Cause the server to enter utility mode, mainly
used in conjection with *FAST.
*LOGOFF <spec>
Will logoff the user specified, or the user at
the station specified. You may specify multiple
users by using commas:
*LOGOFF rick, anna, james, david, amy
or by using wildcards:
*LOGOFF *
will log off everybody except the person typing
this command.
*PGO [<logical printer name>]
Restarts printing after *PSTOP stopped it. This
can be applied to all printers or a specified
printer. The print job current will be
restarted at the beginning.
*PSTOP [<logical printer name>]
Stop printing on the printer specified, or all
printers if none specified. Used if the printer
has jammed, or is producing unwanted output.
The supervisor can *PSTOP and then examine the
print queue.
There is no facility for dealing with users. This is performed with the user editor which should be in a directory called SysProgs within the root of the main drive.
Utility Mode (accessed using the FAST terminal, or by direct serial link) will not be discussed as it is fairly self-explanatory. What will be explained, briefly, is the way that the discs are allocated:
A, B, C & D - Floppy discs, as marked on the back
of the MDFS unit.
E through L - Harddiscs
E - Controller 0, drive 0
F - Controller 1, drive 0
G - Controller 0, drive 1
H - Controller 1, drive 1
I - Controller 2, drive 0
J - Controller 3, drive 0
K - Controller 2, drive 1
L - Controller 3, drive 1
The SCSI devices are allocated as:
0 - harddisc
1 - harddisc
2 - harddisc
3 - harddisc
4 - reserved for tape drive
5 - reserved
6 - reserved
7 - the MDFS (master)
Harddiscs can have partitions. The first partition
is number 1 (NOT zero). Therefore the second
partition on a disc with identity 3 is "J2".
Normal SCSI drives will ONLY support E, F, I and J.
G, H, K and L are only possible with an Adaptec
controller that has a second drive attached.