SUMMARY: 4mm 120 foot cartridge will not store more than 4 MEG even in compressed mode.

From: Steve Poulsen (
Date: Wed Apr 29 1998 - 10:26:53 CDT

The responses came in and for the most part were all in agreement. The
shortest summary is below:

a DDS-1 drive can handle 60 and 90 metre tapes (1.3/2 GB uncompressed)
        - this is the Sun '5Gb' drive
a DDS-2 can in addition handle 120 metre tapes (4Gb uncompressed)
a DDS-3 can in addition handle 125 metre tapes (12Gb uncompressed)

A longer tape should never be put in an earlier type of drive - usually
the media is thinner and the mechanism may strech or break the tape.
Anyway, the extra capacity in general is not achived by longer tape lengths,
but by higher data density.

In short you're stuck with 2Gb.

I messed up using feet instead of meters but everyone understood my
ignorance of tape drives.

Thanks for all the responses. I got several responses which said about the same thing, some with more info or different info. Since I failed to specify Solaris 2.5(or DDS-DC), I received some responses that were correct, but not for Solaris 2.5 (they were related to block size and media length which I don't think apply to Solaris 2.5). Here are some of the responses.

---------------------------------------------------------------------------- ---- What you have is a DDS-2 deck. DDS-2 stores 2Gb native on a 120m tape, or approximately 4Gb compressed, assuming an average 2:1 compression ratio. Actual compressed capacity will vary depending on the compressibility of your data. Highly compressible data might reach 2.5:1, which is where the 5Gb figure comes from, but you are much more likely to see ~2:1. If you are getting 4Gb compressed, you are doing okay. ---------------------------------------------------------------------------- ---- I have a 5GB DAT drive from sun and I called them up once because I did not see an increase in capacity when using a 120m vs a 90m tape. They said that you can use 120m tapes in the drive, but it will be treated as a 90m tape. There is no upgrade available, either firmware or hardware that will convert it to a drive that is capable of utilizing the full 120m of a tape. So, 90m is the max for my drive. ---------------------------------------------------------------------------- ---- Actually, your assumption is incorrect. A 60m-90m tape is DDS, A 120m tape is DDS2. If the drive is a DDS drive (90m) it does not know about DDS2 tapes (which came on the scene after those drives were made). As such, it can not use those tapes for anything more than 0m. ----------------------------------------------------------------------- --------- Wrong assumption... You have a DDS-DC drive, the max it supports is 90m tape. DDS-2 will support a 120M tape.

DAT (& 8mm) are kinda funny that way. (Actually, helical-scan drives in general...) ---------------------------------------------------------------------------- ---- Your tape drive can only take 60 and 90 meter tapes. I'm suprised that it takes 120 meter tapes at all. You're really risking destroying the tape. ---------------------------------------------------------------------------- ---- Incorrect. We have two types of drives: the 8505XL and the Eliant. The biggest tape the 8505XL can use is 112M. The biggest for the Eliant is 160M. Now, the Eliant can *read* 112M tapes, but it can't write to them. The tape capacities are dramatically different:

112M: 5 GB(uncomp) 10 GB(comp) (i think) 160M: 7 GB(uncomp) 14 GB(comp) ---------------------------------------------------------------------------- ---- >From SunSolve: --------------- cut here --------------

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SYNOPSIS: 4mm tape drive matrix DETAIL DESCRIPTION:

4mm Tape Drives

TYPE MAXIMUM TAPE NATIVE ADVERTISED CAPACITY LENGTH (meters) CAPACITY (Gb) W/COMPRESSION (Gb) ------------------------------------------------------------------ Single drives:

DDS-1 60 1.3 [l] 2.6 [m]

DDS-DC 90 2 [l] 5 [m]

DDS-2 120 4 [l] 8 [m]

DDS-3 125 12 [l] 24 [m]

------------------------------------------------------------------- Autoloaders:

DDS-DC 90 8 [l] 16 [m] (4 tape magazine)

DDS-2 120 16 [l] 32 [m] (4 tape magazine)

DDS-3 125 72 [l] 144 [m] (6 tape magazine) -------------------------------------------------------------------


1. Letters in square brackets above are suggested density flags.

2. /dev/rmt density specifiers: typically "l" (low) is used for native mode, and "m" (medium) is used to turn on the compression feature on the drives. Most density specifiers other than "l" will perform compression, but "m" seems to be the convention at Sun.

3. Marketing usually advertises tape drive capacity by assuming a 2:1 compression ratio. In reality, the resulting capacity is generally about 1.8:1 . So for a drive that holds 4Gb in native mode, like the DDS-2, the capacity derived using hardware compression is usually 7Gb. Note that the DDS-DC model was advertised assuming a 2.5:1 ratio instead of the traditional 2:1 ratio.

4. Media is NOT backwards compatible. For example, DO NOT use a 120m tape in an DDS-DC. However, you CAN use a 60m tape in an DDS-2.

5. Identifying the drives: If you don't see any markings on the front of the unit it is most likely a DDS-1 or a DDS-DC. Otherwise, the drive will be identified on the faceplate.

PRODUCT AREA: Hardware PRODUCT: Tape drives SUNOS RELEASE: Solaris 2.x HARDWARE: any


> -----Original Message----- > From: > []On Behalf Of Steve Poulsen > Sent: Tuesday, April 28, 1998 1:41 PM > To: Sun Managers (E-mail) > Subject: 4mm 120 foot cartridge will not store more than 4 MEG even in > compressed mode. > > > I have tried many things and do not even know if compressed > mode is working. > I have a tape drive from Sun that is called a: 5 GB 4mm tape > drive. It > claims it can store 5 GB in compressed mode (upper limit) and 2 GB in > uncompressed mode. > > My assumption is that a tape drive can handle any length of tape. The > 2GB-5GB is for 60 ft tapes and so I put in a 120 ft tape > (which is all I > have). Now, this tape should be 4 GB or max of 10 GB > compressed. I dump > all my systems (total is between 3.5 GB and 4GB) and get a > end-of-tape. > What's wrong. Here are the various devices I tried: > > /dev/rmt/0hn > /dev/rmt/0cn > /dev/rmt/0mbn > > Here are the various dump commands: > > ufsdump 0uc > ufsdump 0ub 127 > > Thanks, > > Steve > ------------------------------------------- ___ > Steve Poulsen / / > Development Engineer / /_ > Transcrypt International /__ / > E-Mail: <> / / > 402-479-8365 // > ------------------------------------------- / > >

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