===== How To Use LDAnnn: Logical Disks =====
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:
[[https://www.digiater.nl/lddriver.html]] (software product description) and\\
[[https://www.digiater.nl/downloads.html]] (downloadable .ZIP files, latest version is V9.7)
Good documentation is available on the above website, and also here:
[[http://h41379.www4.hpe.com/openvms/journal/v6/disk_partitioning_with_lddriver.pdf]]
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.
==== Installing the LDdriver Package ====
Install the LDdriver package this way:
* Download the appropriate LDdriver .ZIP file from the website above.
* Unzip that .ZIP file (using the freeware VMS ''UNZIP'' utility).
* Install the resulting LD*.PCSI product installation kit using ''PRODUCT INSTALL''.
* Read the Release Notes, and invoke the following product startup com-file in your VMS system's SYS$MANAGER:SYSTARTUP_VMS.COM file:
$ @SYS$STARTUP:LD$STARTUP
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: ''Command_summary'', ''Features'', ''Setup'', ''Examples'', ''CREATE'', ''CONNECT'' and ''SHOW''. The primary commands you'll use are ''CREATE'', ''CONNECT'', ''SHOW'' and maybe ''DISCONNECT''.
We'll demonstrate the creation and connection of a new Logical Disk next.
==== Creating Your First LDAnnn: Disk ====
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
NOTE: The /CONTIGUOUS is not required
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.
==== Connecting Your LDAnnn: Disk ====
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 ''xxx'':
$ 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 ''CREATE'' and ''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!
Now, ''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.
==== Initializing Your LDAnnn: Disk ====
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!
==== Mounting Your LDAnnn: Disk ====
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...)
==== Using Your LDAnnn: Disk ====
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$SANDBOX:[000000]
Directory DISK$SANDBOX:[000000]
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 ''[SYSTEM]'' (or ''[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$SANDBOX:[000000]LORIN
Directory DISK$SANDBOX:[000000]
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$SANDBOX:[000000]000000.DIR;1
%BACKUP-S-COPIED, copied DISK$SANDBOX:[000000]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.
==== Clean-up -- Dismount, Disconnect, even Delete, etc. ====
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...
==== Summary of Use Cases ====
To summarize -- Logical Disks are good for:
* Practicing VMS file commands, etc. -- As a learning tool, having one or more sandbox disks available for users (and yourself) to practice in makes it easy and stress-free to learn (“No, you can‟t break anything... play to your heart's content...”).
* Containers for isolation, development and testing -- Need an ODS-5 disk structure without changing the underlying host-ODS-2 disk (or visa versa)? Create a logical disk with the target file system structure.
* Containers for installing a layered product or complete application suite into... without disrupting production use of the real/released-version of that software package. Do you see how the principles of rapid deployment might benefit from this tool/resource?
* Providing very-fine-grained security protection (protection masks, ACLs) both to the LD-container file itself, and to any/all files it contains.
* Any other purpose where containers can be used to isolate, enclose and protect packages of software, project use, or other special-purpose scenarios.