guy@auspex.auspex.com (Guy Harris) (10/03/90)
1) DAT has the notion of a "setmark" as well as a file mark, probably introduced by folks who think tapes are composed of file sets, with file marks between the files and setmarks between the sets. (UNIX doesn't play the game that way.) Does HP-UX write filemarks between files (e.g., between "tar" or "cpio" archives), or setmarks? Is there a consensus among UNIX vendors as to which to use, or is it every vendor for itself? 2) Does HP-UX run DAT drives in fixed-block mode or variable-block mode (i.e., does it turn on the Fixed Size bit in SCSI Read and Write commands)? If it's fixed-block mode, is there a default blocksize? Is there any consensus amoung UNIX vendors here?
tml@tik.vtt.fi (Tor Lillqvist) (10/04/90)
Some more questions about HP's DAT tape (or should we say DDS?): Before we actually got our 822 with DDS tape drive, we heard stories about how fast the DDS tape was supposed to be, especially when searching for a file. Now when I have used it somewhat, I haven't noticed that it would be much faster than, say, a 7980 open-reel tape drive. In what way is a DDS tape supposed to be used to be "fast"? Should files be stored as individual tape files with EOF marks between? -- Tor Lillqvist, working, but not speaking, for the Technical Research Centre of Finland
jarmo@tut.fi (Jarmo Sorvari) (10/04/90)
In article <TML.90Oct3133613@sottuli.tik.vtt.fi> tml@tik.vtt.fi (Tor Lillqvist) writes:
In what way is a DDS tape supposed to be used to be "fast"?
This relates to your question partly: I remember seeing in a brochure
that the "fast search" capability (locating any file within the 1.3 Gb
in something like 15 seconds?!) is supported fully only in HP-UX 8.0.
Maybe someone at HP will confirm/correct this.
--
-----------------------------------------------------------------------------
! Jarmo Sorvari Control Engineering Laboratory !
! jarmo@tut.fi Tampere University of Technology !
--------------------------------------- BOX 527, 33101 Tampere, Finland -----stevej@hpcpbla.HP.COM (Steve Jerman) (10/08/90)
Hi Everyone,
I thought I'd reply to all of the questions in this notes string at
once so:
From guy@auspex.auspex.com:
>1) DAT has the notion of a "setmark" as well as a file mark, probably
> introduced by folks who think tapes are composed of file sets, with
> file marks between the files and setmarks between the sets. (UNIX
> doesn't play the game that way.)
>
> Does HP-UX write filemarks between files (e.g., between "tar" or
> "cpio" archives), or setmarks?
>
> Is there a consensus among UNIX vendors as to which to use, or is it
> every vendor for itself?
The concept of a 'setmark' was introduced in the DDS format as a
another mark heirachically (sp?) superior to the filemark. The idea is
that with such a large amount of data on a tape some extra means of
splitting up 'filesets' was needed. The 'setmark' is supported in the
SCSI-2 specification, which means that SCSI tape drivers can use them if
the need it.
However this is a very new feature and as yet HPUX (and U**X in general) do
not have facilities to use setmarks, especially in conjunction with the
standard utilities such as tar or dd. They still only use filemarks.
This will change in the future as people become used to all the
increased functionality available in the DDS drives and as users such as
yourselves ask for it.
>2) Does HP-UX run DAT drives in fixed-block mode or variable-block mode
> (i.e., does it turn on the Fixed Size bit in SCSI Read and Write
> commands)? If it's fixed-block mode, is there a default blocksize?
>
> Is there any consensus among UNIX vendors here?
With HP-UX, the tape drive is used in variable block mode. This is the consensus
among U**X implementations. The PC (MSDOS) market, however, use fixed mode.
The blocksizes they use are either 512 or 1024, depending on the application.
From tml@tik.vtt.fi Wed Oct 3 18:36:13 1990
>Some more questions about HP's DAT tape (or should we say DDS?):
Well done, the name of the format, which is an extension of the
DAT Audio format, is DDS (Digital Data Storage).
>Before we actually got our 822 with DDS tape drive, we heard stories
>about how fast the DDS tape was supposed to be, especially when
>searching for a file. Now when I have used it somewhat, I haven't
>noticed that it would be much faster than, say, a 7980 open-reel tape
>drive.
>
>In what way is a DDS tape supposed to be used to be "fast"? Should
>files be stored as individual tape files with EOF marks between?
OK you are quite right. If you use tar, cpio etc to back up your whole
system and then try to recover one file, it's not very fast. This
because of the way that the standard utilities work. They just read
the archive until they find the file that you want. In future, fbackup
at least, and probably other utilities will support fast search to
recover files. This means that instead of reading up to the file, the
utilities will know where on tape the file is, and use the SCSI 'SPACE'
command to get there. This *is* fast.
In the mean time if you know a reasonable amount about HP-UX, you can
decrease your access time significantly by making use of the MT(1)
command. You can do this as follow:
o Use 'cpio' to do your backing up (Fbackup always starts at BOT).
o Split up your file system into separate chunks (using mt between
separate cpio backups)
o Use the 'mt fsf' command (which uses fast search) to get to the right cpio
archive.
o restore the file using the cpio command on just that small archive.
If the above method is used intelligently single file restores can be
very quick, even at the end for the tape.
Here's an example
#!/bin/ksh
# Demo to show use on mt and cpio on DDS drive.
set -x
TAPE=/dev/rmt/5.norew # for my drive (major num 54, minor num 0x0e0503)
DIR1=/bin
DIR2=/etc
DIR3=/usr/lib
#backup /bin
#rewind tape
mt -t $TAPE rew
#backup directories
for dir in $DIR1 $DIR2 $DIR3
do
find $dir -print | cpio -oB > $TAPE
mt -t $TAPE eof # write 2 filemarks
mt -t $TAPE bsf 1 # back space over one of them
# leaves a separator and also flushes buffer to tape
done
#now rewind
mt -t $TAPE rew
# space out 2 filemarks - to the lib directory
mt -t $TAPE fsf 2
# and read the directory
cpio -iBt < $TAPE
From jarmo@tut.fi Thu Oct 4 09:52:20 1990
>In article <TML.90Oct3133613@sottuli.tik.vtt.fi> tml@tik.vtt.fi (Tor Lillqvist) writes:
>
> In what way is a DDS tape supposed to be used to be "fast"?
>
>This relates to your question partly: I remember seeing in a brochure
>that the "fast search" capability (locating any file within the 1.3 Gb
>in something like 15 seconds?!) is supported fully only in HP-UX 8.0.
>Maybe someone at HP will confirm/correct this.
The "fast-search" time of 20 seconds you mention is derived as follows. It
takes 40 seconds to move from one end of a 60 metre, 1.3 GByte DDS tape to the
other end at 200x read speed. So on average you can reach any point in 20
seconds. In practice it takes longer to actually complete the operation
because of overheads such as reading the tape etc. However any point on the
tape can be reached in between 10 and 60 seconds.
I believe there are plans to add this support to HPUX 8.0
Steve Jerman
Address: Email:
Filton Road stevej@hpcpbla.bri.hp.com
Stoke Gifford
Bristol
BS12 6QZ
UK
Phone: Fax:
(44) 272 799910 x22424 (44) 272 236091
---
working, but not speaking, for Hewlett Packard