rtp1@tank.uchicago.edu (raymond thomas pierrehumbert) (01/12/90)
Another elementary question: If I am running BSD4.3 under Domain, can I use tar instead of wbak/rbak to read and write cartridge tapes? Do I use ct0 as my device? Can it be used for backups? What is the advantage of wbak/rbak over tar?
krowitz%richter@UMIX.CC.UMICH.EDU (David Krowitz) (01/12/90)
tar can be used with /dev/rct8 or /dev/rct12 (auto rewind vs. not auto rewind). tar sometimes will not work if it doesn't think that the tape has been rewound. Use "mt -f /dev/rct8 rewind" or "/com/rbak -dev ct -rewind" in this case. The major advantage of wbak/rbak over tar is that the Apollo-specific utilities will 1) handle multi-tape backups -- tar will bomb if the directory will not fit on a single tape. 2) will restore directories with names other than the original. If you save /somedir/otherdir/my_dir with tar, you must restore it to the exact same directory. If the machine you are restoring on does not have the /somedir/otherdir directory it will have to be created. wbak/rbak will let you change the name as you restore the tape. 3) On SR9.7 systems, tar will not store the Apollo file types on the tape. Executable files will no longer be executable when restored. On SR10 systems there is a new -A switch which will get around this problem. -- David Krowitz krowitz@richter.mit.edu (18.83.0.109) krowitz%richter.mit.edu@eddie.mit.edu krowitz%richter.mit.edu@mitvma.bitnet (in order of decreasing preference)
arane@me.utoronto.ca (Raphael Arane) (01/12/90)
In article <7125@tank.uchicago.edu> rtp1@tank.uchicago.edu (raymond thomas pierrehumbert) writes: >Another elementary question: If I am running BSD4.3 under Domain, >can I use tar instead of wbak/rbak to read and write cartridge tapes? >Do I use ct0 as my device? Can it be used for backups? What is the >advantage of wbak/rbak over tar? My answer pertains to BSD4.2 and SR9.7, but it's probably still correct. For a cartridge tape I use /dev/rct8. Practically always my 'tar' fails to recognize the tape drive on the first attempt, so I have to "wake it up" using /com/rbak -reten, for example. I find tar much-much slower than wbak/rbak, therefore I use it exclusively for information exchange with Suns, for example. For backups I stick with the wbak. Actually I'd like to know why tar is so slow compared with the Aegis feature - anybody out there to enlighten us? -- Rafi Arane.
krowitz%richter@UMIX.CC.UMICH.EDU (David Krowitz) (01/13/90)
Tar uses much smaller blocks, by default, that wbak/rbak does. The default block size for tar is 512 bytes. tar is probably also using Unix I/O streams, which are much slower than using memory mapped I/O as wbak/rbak do. -- David Krowitz krowitz@richter.mit.edu (18.83.0.109) krowitz%richter.mit.edu@eddie.mit.edu krowitz%richter.mit.edu@mitvma.bitnet (in order of decreasing preference)
lampi@pnet02.gryphon.com (Michael Lampi) (01/13/90)
Sure, go ahead and use tar to read/write from the cartridge tape drive instead
of wbak/rbak. You can generally use tar to interchange cartridge tape files
with other unix systems and Apollo's.
Use ct0 as the device.
If you like tar for backups there is no reason it can not be used for such.
The main advantages of wbak/rbak over tar, especially with cartridge tape, are
that ACL's are saved, the throughput is higher, and directory structures are
preserved. There are a couple of additional features that I like, but they may
not be as important to you; e.g., automatic backup history files in each
directory (if desired), modified/created date filters, etc.
Michael Lampi MDL Corporation 213/782-7888 fax 213/782-7927
UUCP: {ames!elroy, <routing site>}!gryphon!pnet02!lampi
INET: lampi@pnet02.gryphon.com
"My opinions are that of my corporation!"hanche@imf.unit.no (Harald Hanche-Olsen) (01/13/90)
Like David Krowitz says, tar can be used with /dev/rct8 or /dev/rct12 (auto
rewind vs. not auto rewind)... except, in my experience, it rewinds the tape
afterwards using either device. I have even checked it out:
% /etc/edmtdesc /dev/rct12 -l
Volume information:
dev (device type) ct
u (tape unit #) 0
lab (labeled) no
reo (reopen previously used volume) yes
clv (close volume on file-close) yes
spos (save position on volume-close) yes
File information:
f (file sequence #) current
rf (record format) F (fixed length)
bl (block length) 512
rl (record length) 512
ascnl (ascii newline handling) no
Has anyone managed to write multiple tar files on a single cartridge?
- Harald.Hanche-Olsen@imf.unit.nolampi@pnet02.gryphon.com (Michael Lampi) (01/18/90)
lampi@pnet02.gryphon.com (Michael Lampi) writes: >Sure, go ahead and use tar to read/write from the cartridge tape drive instead >of wbak/rbak. You can generally use tar to interchange cartridge tape files >with other unix systems and Apollo's. > >Use ct0 as the device. > Ooops! Sorry about device "ct0" -- guess I was too wrapped up in device driver writing and forgot about the "rct#" pseudo-devices. BTW, if you use edmtdesc you can create your own tape "device" names, each with their own attributes. So, potentially, you could come up with a /dev/ct in place of /dev/rct8, which is there jlru. Michael Lampi MDL Corporation 213/782-7888 fax 213/782-7927 UUCP: {ames!elroy, <routing site>}!gryphon!pnet02!lampi INET: lampi@pnet02.gryphon.com "My opinions are that of my corporation!"