Logical Disks, presented in OpenVMS as LDAnnn: devices, are one of the operating system's best-kept secrets, even though there's really no conspiracy. Implemented as a Files-11 file system inside of a “container file,” logical disks can often serve as a solution to problems (or opportunities) you haven't yet known you face.
Logical Disks (sometimes also called Virtual Disks in this VMS context, although both terms have other technical meanings in other environments) are implemented using the freeware LDdriver layered product, available for VAX, Alpha and Integrity platforms for free here:
Good documentation is available on the above website, and also here:
Among various other uses, Logical Disks can be used as a “sandbox” (playground) VMS disk for training new users (where they cannot “hurt anything”), as well as for an ODS-5 structured Files-11 volume (e.g., on an ODS-2 volume) for installation of and/or experimentation with open source software.
Install the LDdriver package this way:
This layered software product installation adds a new DCL command, LD, to SYS$LIBRARY:DCLTABLES.EXE. To pick up this command for immediate use, you can either logout and log-back-in again, or just issue this command:
$ SET COMMAND /TABLE=SYS$LIBRARY:DCLTABLES
Once you've got the new LD command at your process's disposal, explore LD HELP this way:
$ LD HELP LD The logical disk utility is a system management tool available to any user for controlling logical disk usage. A Logical Disk is a file available on a Physical Disk, which acts as a real Physical Disk (the file may or may not be contiguous). The Logical Disks are available in any directory of the Physical Disk. A large disk can be divided into smaller sections, each a Logi- cal Disk, supporting the same I/O functions as the Physical Disk. By giving the Logical Disk File a good protection level and mounting it private or with device protection, you are able to add a number of protection levels to your file system. The logical disk is controlled by the LD utility, which can be directly invoked from DCL. Format: LD [/qualifiers] [Filespec] [Device] Additional information available: Author Command_summary Driver_functions Error_messages Features HELP New_features_V5.0 New_features_V5.1 New_features_V6.0 New_features_V6.2 New_features_V6.3 New_features_V7.0 New_features_V8.0 New_features_V8.1 New_features_V8.2 Parameters Privileges_and_Quotas Restrictions Setup IO_Trace_example CONNECT CREATE DISCONNECT NOPROTECT NOWATCH SHOW TRACE NOTRACE PROTECT WATCH VERSION Examples LD Subtopic?
Explore these help topics at least:
SHOW. The primary commands you'll use are
SHOW and maybe
We'll demonstrate the creation and connection of a new Logical Disk next.
Let's start by creating a “sandbox” (or “playpen”) Logical Disk file, just to fool around with, in a user's home directory ― the size of 50,000 is arbitrary, but plenty big enough for experimentation:
$ SHOW DEFAULT DSA2:[LRICKER] $ LD CREATE /SIZE=50000 /CONTIGUOUS /LOG DSA2:[LRICKER]SANDBOX.DSK %LD-I-CREATED, File DSA2:[LRICKER]SANDBOX.DSK;1 created
This just creates a big file, with no actual contents other than whatever “junk data” was previously in the disk blocks allocated to this file. Note that, although we've used .DSK as the file extension in this example, you can use whatever file extension you like, as there's no specific file-type enforced. However, stick to a filename and type that is conventional and “obvious.”
$ DIRECTORY /SIZE /DATE /OWNER /PROT *.DSK Directory DSA2:[LRICKER] SANDBOX.DSK;1 50000 2-AUG-2017 08:21:25.30 [STAFF,LRICKER] (RWED,RWED,,) Total of 1 file, 50000 blocks.
The LD-container file needs to be created just once, of course – once created, it can be connected and mounted numerous times, whenever needed. The container file can also be disconnected from the LD-driver and summarily deleted, if you're sure you're done with it… You can “start over again.” Of course, you can have as many Logical Disks (files) as you practically need.
Once created, this Logical Disk file next has to be connected to an actual
LDAxxx: device (based on the LDA0: template device), so we have to find an unused unit number
$ SHOW DEV LD Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt $254$LDA0: (CLASS8) Online 0 $254$LDA10: (CLASS8) Online 0 $254$LDA11: (CLASS8) Online 0 $254$LDA12: (CLASS8) Online 0 ... $254$LDA19: (CLASS8) Online 0 $254$LDA101: (CLASS8) Online 0 $254$LDA102: (CLASS8) Online 0 ... $254$LDA109: (CLASS8) Online 0 $254$LDA200: (CLASS8) Mounted 0 OPENSOURCE 5641984 1 2 $254$LDA1024: (CLASS8) Mounted 0 RUBYMINE 29500 1 1
On our CLASS8 training system here at PARSEC, we play with numerous Logical Disks, so we've got lots. Your mileage will vary, and to begin with, you'll likely show no
LDAnnn: devices on your system – this will be your first. On a system with existing
LDAnnn: devices, pick a totally new, unused unit number.
Because it's easy(er) to remember and type, let's use
LDA77: for our experiments. This will likely be a temporary use for this particular unit number – if you ever decide to “go to production” or other regular, persistent use for a particular Logical Disk, be sure to more-or-less permanently allocate an
LDAxxx: (unit number) to that LD-file; likely, you'll put all of that into a startup command file for consistency.
$ LD CONNECT /LOG DSA2:[LRICKER]SANDBOX.DSK LDA77: LDISK$SANDBOX %LD-I-CONNECTED, Connected $254$LDA77: to DSA2:[LRICKER]SANDBOX.DSK;1
We're making consistent use of the
/LOG qualifier for these LD-commands just to show what's happening… this qualifier is optional.
Note: Experience shows that the LD
CONNECT (and, by extension, the
DISCONNECT) commands are particular, picky even, about the colon “:” on the end of the LDAxxx: device name – Don't omit that colon!
LDA77: is a device that just happens to be “backed by” (or implemented as) a file. Since this file has just been created, it has no valid contents – and certainly does not yet have a file system in it. So this:
$ SHOW DEVICE LDA77: /FULL Disk $254$LDA77: (CLASS8), device type Foreign disk type 1, is online, file- oriented device, shareable, available to cluster. Error count 0 Operations completed 2 Owner process "" Owner UIC [SYSTEST,SYSTEM] Owner process ID 00000000 Dev Prot S:RWPL,O:RWPL,G:R,W Reference count 0 Default buffer size 512 Total blocks 20000 Sectors per track 11 Total cylinders 152 Tracks per cylinder 12 Allocation class 254
…simply shows us a “foreign device,” un-mounted and un-loved. This device needs to be initialized with a file system.
We do this next command – not surprisingly, an INITIALIZE command – once (per newly-created LD-device)… Note that this command does not initialize the file, it initialized the device. Whenever we create a new LD-container file and connect it, we need to next initialize its file system (contents). Be sure to give the file system a meaningful volume label; you can choose either a Files-11 ODS-2 (default, or
/STRUCTURE=2) or ODS-5 (extended file system,
/STRUCTURE=5) file system:
$ INITIALIZE /STRUCTURE=5 LDA77: SANDBOX
Note that you can create an ODS-5 Logical Disk (file) on a host-disk that is itself an ODS-2 file structure (or visa-versa); this gives you considerable flexibility!
Now, let's mount it and then look at the device's structure:
$ MOUNT LDA77: SANDBOX SANDBOX %MOUNT-I-MOUNTED, SANDBOX mounted on _$254$LDA77: (CLASS8) $ SHOW DEVICE /FULL LDA77: Disk $254$LDA77: (CLASS8), device type Foreign disk type 1, is online, mounted, file-oriented device, shareable. Error count 0 Operations completed 530 Owner process "" Owner UIC [STAFF,LRICKER] Owner process ID 00000000 Dev Prot S:RWPL,O:RWPL,G:R,W Reference count 1 Default buffer size 512 Total blocks 50000 Sectors per track 13 Total cylinders 190 Tracks per cylinder 13 Logical Volume Size 50000 Expansion Size Limit 53248 Allocation class 254 Volume label "SANDBOX" Relative volume number 0 Cluster size 1 Transaction count 1 Free blocks 49886 Maximum files allowed 12000 Extend quantity 5 Mount count 1 Mount status Process Cache name "_$32$DKA0:XQPCACHE" Extent cache size 64 Max blocks in extent cache 4988 File ID cache size 64 Blocks in extent cache 0 Quota cache size 0 Maximum buffers in FCP cache 2239 Volume owner UIC [STAFF,LRICKER] Vol Prot S:RWCD,O:RWCD,G:RWCD,W:RWCD Volume Status: ODS-5, subject to mount verification, file high-water marking, write-through XFC caching enabled, write-back XQP caching enabled, special files enabled.
That's much better. As usual, the MOUNT command gives us “free” volume logical names to use for this new “disk”:
$ SHOW LOGICAL /FULL *SANDBOX* (LNM$PROCESS_TABLE) [kernel] [no protection information] (LNM$JOB_859BE4C0) [kernel] [shareable] [Quota=(44672,50000)] [Protection=(RWCD,RWCD,,)] [Owner=[STAFF,LRICKER]] "LDISK$SANDBOX" [super] = "$254$LDA77:" "SANDBOX" [super] = "$254$LDA77:" (LNM$GROUP_000007) [kernel] [shareable,group] [Protection=(RWCD,R,R,)] [Owner=[STAFF,*]] (LNM$SYSTEM_TABLE) [kernel] [shareable,system] [Protection=(RWC,RWC,R,R)] [Owner=[SYSTEST,SYSTEM]] ...
And where did those logical names “
DISK$SANDBOX” and “
SANDBOX” come from? (Left as an exercise to the reader…)
With this disk initialized (once only) and mounted (whenever we want and need to do so), we can now treat it just like any other disk device (or, more properly, volume) and examine its contents.
$ DIRECTORY /SIZE /DATE /PROTECTION DISK$SANDBOX: Directory DISK$SANDBOX: 000000.DIR;1 1 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,E) BACKUP.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) BADBLK.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) BADLOG.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) BITMAP.SYS;1 14 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) CONTIN.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) CORIMG.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) GPT.SYS;1 68 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,E) INDEXF.SYS;1 19 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) SECURITY.SYS;1 1 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) VOLSET.SYS;1 0 2-AUG-2017 08:57:33.72 (RWED,RWED,RE,) Total of 13 files, 103 blocks.
because that previous
INITIALIZE command did not use the
/SYSTEM qualifier, this LD-volume is owned by the user, not by
[1,4]). This may or may not be a problem for a particular use case, so just be aware of the options involved here, just like for any other disk/device/volume.
Let's use this new volume – exercise it with a few file commands:
$ CREATE /DIRECTORY /OWNER=PARENT /LOG DISK$SANDBOX:[LORIN] %CREATE-I-CREATED, DISK$SANDBOX:[LORIN] created $ DIRECTORY /SIZE /DATE /OWNER /PROTECTION DISK$SANDBOX:LORIN Directory DISK$SANDBOX: LORIN.DIR;1 1 2-AUG-2017 09:07:34.95 [STAFF,LRICKER] (RWE,RWE,RE,E) Total of 1 file, 1 block.
So far, so good!… It seems to work just like a “real disk”… as it should. More:
$ SET DEFAULT disk$sandbox:[lorin] $ SHOW DEFAULT DISK$SANDBOX:[LORIN] $ copy /log SYS$LOGIN:LOGIN.COM  %COPY-S-COPIED, DSA2:[LRICKER]LOGIN.COM;14 copied to DISK$SANDBOX:[LORIN]LOGIN.COM;14 (2 blocks)
I hope you weren't expecting magic or miracles ― it really works quite normally…
$ copy LOGIN.COM  $ copy LOGIN.COM  $ copy LOGIN.COM  $ purge /log LOGIN.COM %PURGE-I-FILPURG, DISK$SANDBOX:[LORIN]LOGIN.COM;16 deleted (2 blocks) %PURGE-I-FILPURG, DISK$SANDBOX:[LORIN]LOGIN.COM;15 deleted (2 blocks) %PURGE-I-FILPURG, DISK$SANDBOX:[LORIN]LOGIN.COM;14 deleted (2 blocks) %PURGE-I-TOTAL, 3 files deleted (6 blocks)
Seen enough? Can you make one of these work for your own practice sessions, learning, and …maybe… find a way to exploit this in some production scenario?
Oh, just one more thing…
$ BACKUP DISK$SANDBOX:[*...]*.*;* SYS$LOGIN:SANDBOX_SAFETY.BCK /SAVE /LOG %BACKUP-S-COPIED, copied DISK$SANDBOX:000000.DIR;1 %BACKUP-S-COPIED, copied DISK$SANDBOX:LORIN.DIR;1 %BACKUP-S-COPIED, copied DISK$SANDBOX:[LORIN]LOGIN.COM;17
Now we've got a backup save-set for safety, just in case we want to recover our sandbox disk in the future.
Well, since this is just a practice session, how do we get rid of the evidence? How do we clean up? Just like this…
$ SET DEFAULT sys$login $ SHOW DEFAULT DSA2:[LRICKER] $ $ DISMOUNT LDA77: $ LD DISCONNECT /ABORT LDA77: $ DELETE SANDBOX.DSK;1 /LOG %DELETE-I-FILDEL, DSA2:[LRICKER]SANDBOX.DSK;1 deleted (50112 blocks)
Dismounting an LD-disk is just dismounting a disk device. Read about the LD
DISCONNECT /ABORT qualifier – usually unneeded, unless there are pesky multi-user connections that won't “let go”. The
DELETE command makes the sandbox file good and truly gone. But easily recreated…
To summarize – Logical Disks are good for: