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OpenVMS doesn't have an "undelete" function. However, if you are quick to write-protect the disk or if you can guarantee that no new files get created or existing files extended, your data is still on the disk and it may be possible to retrieve it. The FLORIAN tool available from various websites can potentially recover the file, see question Section 13.1 for pointers. Other alternatives here include the DFU tool, available on the OpenVMS Freeware CD-ROM distribution.
If you are setting up a user environment for yourself or for others, it is quite easy to use DCL to intercept the DELETE command, using a symbol:
$ DEL*ETE :== @SYS$LOGIN:MYDELETE.COM |
The DELETE symbol will cause the procedure to be invoked whenever the
user enters the DELETE command, and it can copy the file(s) to a
"trashcan" subdirectory before issuing a "real"
DELETE on the files. Other procedures can retrieve the file(s) from the
"trashcan" subdirectory, and can (and should) clean out the
"trashcan" as appropriate. (Realize that this DELETE symbol
can interfere with DELETE/GLOBAL and other similar DCL commands.)
9.2 Why does SHOW QUOTA give a different answer than DIR/SIZE?
DIRECTORY/SIZE doesn't take into account the size of file headers which are charged to your quota. Also, unless you use DIRECTORY/SIZE:ALL, you will see only the "used" size of the file, not the allocated size which is what gets charged against your quota. Also, you may have files in other directories.
$ DIRECTORY/SIZE=ALL/GRAND [username...] Grand total of D1 directories, F1 files, B1/B2 blocks. $ DIRECTORY/SIZZ=ALL/GRAND [-]username.DIR Grand total of 1 directory, 1 file, B3/B4 blocks. $ SHOW QUOTA User [username] has B5 blocks used, B6 available of B7 authorized and permitted overdraft of B8 blocks on disk |
If the user has no files in other directories and all file-headers are only 1 block, then the following should apply:
B5=B2+B4+F1+1 |
If the diskquota has drifted out of synchronization, then the system-manager can force a quota rebuild---due to various factors, the quota file can potentially drift from the actual use over time, and a periodic rebuild can be performed at appropriate intervals.
Also be aware that the DIRECTORY/SIZE command can report larger values
than might otherwise be expected when used to evaluate files and/or
directories that are alias links---such as the system roots on OpenVMS
system disks---as the command reports a total that is cumulative over
all of the files and directories examined, without regard for which
ones might be alias entries and which are not. (In other words, a
DIRECTORY/SIZE of an entire OpenVMS system disk will report a disk
useage value larger than the (usually more accurate) value reported by
the SHOW DEVICE command. This as a result of the alias entries linking
each SYS$SYSDEVICE:[SYSCOMMON]SYS*.DIR directory file and the
SYS$SYSDEVICE:[000000]VMS$COMMON.DIR file together.)
9.3 How do I make sure that my data is safely written to disk?
If your application must absolutely guarantee that data is available, no matter what, there's really no substitute for RMS Journaling and host- or controller-based shadowing. However, you can achieve a good degree of data integrity by issuing a SYS$FLUSH RMS call at appropriate times (if you're using RMS, that is.) If you're using a high-level language's I/O system, check that language's documentation to see if you can access the RMS control blocks for the open file. In C you can use fflush followed by fsync.
For details on disk bad block handling on MSCP and on SCSI disk devices, please see Ask The Wizard (ATW) topic (6926).
For additional information on the OpenVMS Ask The Wizard (ATW) area and
for a pointer to the available ATW Wizard.zip archive, please see
Section 3.9.
9.4 What are the limits on file specifications and directories?
A file specification has an aggregate maximum size of 255 characters at present. The node and device specification may be up to 255 characters each - file name and file types may be up to 39 characters each. File versions are from 1 through 32767, though 0 (latest version), -0 (oldest version) and -n (n'th previous version) can be used in most contexts. A file specification may not have more than 8 directories and subdirectories - while it is possible to create subdirectories of greater depth, accessing them is problematic in most cases and this should be avoided.
Application developers should use OpenVMS-supplied routines for parsing file specifications - this ensures that changes in what is allowable will not tend to break your application. Consider that various parts of the file specification may contain quoted strings with embedded spaces and other punctuation! Some routines of interest are SYS$FILESCAN, SYS$PARSE and LIB$TRIM_FILESPEC. For further information, see the OpenVMS Guide to File Applications.
Performance of larger directory files improves (greatly) with OpenVMS V7.2 and later---operations on directory files of 128 blocks and larger were rather slower on earlier OpenVMS releases due to the smaller size of the directory cache and due to the directory I/O processing logic.
For fastest directory deletions, consider a reverse deletion---delete
from the last file in the directory to the first. This reversal speeds
the deletion operation by avoiding unnecessary directory I/O operations
as the files are deleted. Tools such as the Freeware DFU can be used
for this purpose,
as can various available reverse-DELETE DCL command procedures.
9.5 What is the largest disk volume size OpenVMS can access?
One Terabyte (TB; 2**31 blocks of 2**9 bytes; 0x07FFFFFFF blocks). 255 volumes in a volume set. The largest contiguous allocation possible for any particular file is 0x03FFFFFFF blocks.
Prior to the release of V6.0, the OpenVMS file system was limited to disk volumes of 8.38 GB (2**24 blocks, 16777216 blocks) or less.
On some systems, there are restrictions in the console program that limit the size of the OpenVMS system disk. Note that data disks are not affected by console program limits. For example, all members of the VAXstation 3100 series are limited to a system disk to 1.073 GB or less due to the console, though larger data disks are possible. This limit due to the SCSI drivers used by and built into the console ROM to read the OpenVMS bootstrap files, and these same drivers are also used by OpenVMS to write the system crashdump.
There are numerous discussions of this VAXstation 3100 in the comp.os.vms newsgroup archives. Please use Google newsgroup search to search the archives for further details, for discussions of the workarounds, and for details of the potential for a simple failed bootstrap and particularly for discussions of the potential for severe system disk corruptions on crashes.
Some SCSI disks with capacities larger than 8.58 gigabytes (GB) will require the use of an OpenVMS ECO kit (eg: ALPSCSI04_062 or later; see Section 14.26 for details) for new SCSI device drivers. Failure to use this ECO can cause "rounding errors" on the SCSI disk device capacity---OpenVMS will not use nor display the full capacity of the drive---and "%sysinit-e-error mounting system device status equals 000008C4" (8C4 -> "%SYSTEM-?-FILESTRUCT, unsupported file structure level") errors during bootstrap. (One workaround for the bootstrap when the bitmap is located far into the disk is the use of INIT/INDEX=BEGIN.) The problem here involves the particular extensions and fields used for larger capacity disks within the SCSI specifications and within the various intepretations of same.
For ATA (IDE) disk drives:
See Section 14.4.4.2 for additional ATA SYS$DQDRIVER information.
Be aware that a known restriction in certain older versions of the Alpha SRM Console prevents booting most ATA (IDE) drives larger than 8.455 GB, depending on exactly where the various files are located on the volume. Updated SRM consoles for systems with SRM and ATA (IDE) drive support are (will be) available. (OpenVMS Engineering has successfully bootstrapped 20GB ATA (IDE) disks using the appropriate SRM console version.)
All disk-related listed in this section are stated in units of "disk (base ten) gigabytes" (1 GB = 10^9 bytes) and not in units of "software (base two) gigabytes" (1 GB = 2^30; 1 GB = 1073741824.) bytes. Please see Section 14.26 for details of the nomenclature and of the units. |
Be aware that larger disks that are using an extension of SCSI-2--- disks that are using a mode page field that the SCSI-2 specifications normally reserved for tape devices---to permit a larger disk volume size will require a SCSI driver update for OpenVMS, and this change is part of V7.1-2 and later, and also part of ALPSCSI07_062 and later. (These larger disks disks will typically report a DRVERR, or will see the volume size "rounded down".) SCSI disks larger than 16777216 blocks cira 8.455 GB (base ten); 8GB (base two) require this ECO, or require the use of OpenVMS Alpha V7.1-2 or later.
Applications written in C can be limited to file sizes of two gigabytes and less, as a result of the use of longword values within C file operations, and specifically off_t. This restriction is lifted in OpenVMS V7.3-1 and later, and with the application of the C ECO kits available for specific earlier releases. The use of a longword for off_t restricts applications using native C I/O to file sizes of two gigabytes or less, or these applications must use native RMS or XQP calls for specific operations.
Also see Section 14.14, Section 14.26.
9.6 What is the maximum file size, and the RMS record size limit?
RMS can store individual files of a size up to the maximum supported volume size. Under OpenVMS V6.0 and later, the volume size and the RMS maximum file size limit is 2**31 * 512 bytes---one terabyte (1 TB).
"Use a volume set to provide a large, homogeneous public file space. You must use a volume set to create files that are larger than a single physical disk volume. (The file system attempts to balance the load on the volume sets, for example, by creating new files on the volume that is the least full at the time.)"
"You can add volumes to an existing volume set at any time. The maximum number of volumes in a volume set is 255."
The RMS formats---sequential, relative, and indexed---are limited by the one terabyte maximum volume size. RMS relative files are further limited to a number of records that will fit in 32 bits---4 billion records. Sequential and indexed formats do not have a record limit.
Also see Section 2.17.1, Section 14.26.
9.7 How do I write CD-Recordable or DVD media on OpenVMS?
How to create CD-R, CD-RW, DVD-R, DVD+R, DVD-RW, or DVD+RW media on OpenVMS?
Alternatively, consider the following command on OpenVMS Alpha V7.3-1 and later:
@SYS$MANAGER:CDRECORD.COM HELP |
While folks have had success getting PC-based CD-R/RW or DVD-R/RW or DVD+R/RW tools to work with OpenVMS partitions, it is far easier and more reliable to use the OpenVMS-based versions of these tools and directly-attached devices. If you use a Windows-based tool, you will want to specifically select its raw mode, image mode, or block-copy mode, depending on the terminology within the particular tool. The transfer mode and selections is variously refered to as a disk-at-once (DAO) 2048-byte block ISO Mode 1 raw/image/block data disk recording mode.
More details: Creation of CD recordable or DVD recordable media under OpenVMS typically involves one of two approaches: the use of the optional CD-R (`Scribe') capabilities available for the InfoServer or other "offline" hardware packages (PC-based packages will be included in this), or the use of a host-based package such as the CDRECORD or CDWRITE13_VMS or other utilities, including OpenVMS ports of common open-source tools made available by Dr. Eberhard Heuser-Hofmann and various others. Commercial packages and options are also available. Dr. Heuser-Hofmann has DVDwrite , a commercial package which can record DVD media. (
OpenVMS can read ODS-2, ODS-5, and ISO-9660 format CD-ROMs. (If you are very careful, you can create a dual-format CD-R; a CD-R with both ODS-2 and ISO-9660 or both ODS-5 and ISO-9660 or both.)
InfoServer hardware configurations are no longer available from HP, but may potentially be acquired through other means; as used equipment. InfoServer support also has very specific CD-R recording device prerequisites, and these recording devices are no longer generally available.
Packages related to the use of DVD archiving are also available, see the multi-volume capabilities of the DVDarchive/restore Freeware.
http://www.geocities.com/SiliconValley/Lakes/9999/vmscdwri.html |
Additional information is available at the following sites:
U.S. Design offers a package that includes the tools necessary to create a CD or DVD-R with either ISO-9660 or ODS-2 format, for standalone CD-R/RW, DVD-R, or DVD+R/RW drives, for recent OpenVMS versions. Details are available at:
Also see Section 9.7.2 for details on access to recorded media on older
CD-ROM drives.
9.7.1 CD and DVD notation, terminology?
CD-ROM is pre-recorded Compact Disk media, and is the original and oldest CD format. The original CD media was physically stamped, a recording process that is now largely reserved to the highest-volume media reproduction requirements.
CD-R is CD Recordable, a write-once storage medium that can be read by all but the oldest of CD drives; a format which can be read and often even recorded by most CD-RW drives.
CD-RW is CD ReWritable, a format which is readable by many CD drives and by most CD-R drives, and with media that can be recorded and re-recorded by CD-RW drives.
CD media recording speeds are listed as multiples of 150 kilobytes per second, so a 10X drive records at 1500 kilobytes (1.5 megabytes) per second. 600 MB (70 minutes) and 700 MB (80 minutes) recording capacities are both widely available. The minutes designation is derived from the traditional audio-format recording capacity of the particular media.
DVD-R/RW is the older of two common Digital Versatile Disk recording formats, and the DVD-R Recordable or DVD-RW ReWritable media can be read by many DVD drives. As with CD-R formats in older CD drives, older DVD and particularly first-generation DVD players may have problems reading this media format.
DVD+R/RW is the newer of the two common Digital Versatile Disk recording formats, and the DVD+R Recordable or DVD+RW ReWritable media can be read by many DVD drives. Akin to DVD-R/RW media, older and particularly first-generation DVD drives can have problems reading this media format.
The DVD Plus-series drives and media tend to record faster than Minus drives, as (as of this writing) the Plus (+) drives do not require an initial media formatting pass and the Minus (-) drives do. While the appropriate Plus (+) or Minus (-) DVD raw media must be chosen for the particular DVD recorder (and DVD recording drives that are compatible with and capable of using both Plus and Minus media are available), the resulting recorded media is generally readable (playable) in all recent DVD drives and DVD players, regardless of type. (Compatibility is best within the same media-series devices of course, but be certain to verify compatibility across devices regardless of the particular device or particular recording media chosen.)
Presently Plus (+) media is slightly more expensive than Minus (-), but with the prices of all CD and all DVD media continuing to consistently fall, the differences in DVD media costs are becoming irrelevent for all but the production of huge volumes of DVD media.
The rated DVD recording speeds are in multiples of 1353 kilobytes per second, thus a DVD 1X drive is roughly equivalent to a CD 9X drive in I/O requirements and transfer speed.
DVD drive recording speed can and does vary. DVD disk drive recording
speed is limited by the rated recording speed of the media used, so the
slower (and cheaper) DVD media will not record any more quickly in a
faster drive. A 2.4X DVD drive loaded with 1X media will record at 1X.
9.7.2 Use of RRD42 and other older (embossed-media) CD drives?
The RRD42 series SCSI CD-ROM drive is sufficiently old that it can have problems processing CD-R and CD-RW media. Other very old CD drives can have equivalent media compatibility problems when attempting to read (much) newer CD media and newer CD media technologies. These older CD drives are generally intended for use with the so-called embossed media, rather than with non-embossed recorded (recordable) media now in common circulation.
Please consider using a slightly-less-ancient CD-ROM or CD-R or CD-RW drive when working with non-embossed recorded CD media.
To paraphrase one knowledgable---though deliberately nameless---storage engineer, "The RRD42 drive is just past the drooling idiot stage".
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