Networker

Re: [Networker] Calculating optimal paralelism and target session values

2004-01-20 17:14:02
Subject: Re: [Networker] Calculating optimal paralelism and target session values
From: Darren Dunham <ddunham AT TAOS DOT COM>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Tue, 20 Jan 2004 14:14:01 -0800
> To repeat myself; the problem with the DLT4000 is data underrun. It
> runs out of data to write to the tape. The data dries out during
> compression of text or text like data. The interface is not able to
> deliver uncompressed data fast enough. If you want to be able to
> stream a DLT4000 at all times, you must turn off hardware compression.

Obviously it depends on the data coming in.  3MB/s is pretty small for
most systems these days and not a chore to fill.

For the OP with the 10Mb/s link, yeah, that'll be a stretch either
compressed or uncompressed.

> The DLT7000 solves this problem by having a larger buffer and if
> neccessary; writing data before it is completely compressed. It tries
> to keep the tape streaming regardless. It means that less get written
> to the tape.

I've never seen a DLT7000 that did the "don't compress at low speeds"
trick.  That was only on very early models, and even the ones I used
back in 1998 were the 8MB model.

(From an old post I made...)
> This behavior applies only to those DLT7000 models with 4MB cache
> buffer. Very few of these models were released into the market. The
> designation for the DLT7000 models is TH6XY-ZZ, where "X", "Y", and
> "ZZ" represent model variations. The model designation for the DLT7000
> with 4MB cache have either an letter A or B for the "Y" variable. All
> other models have 8MB cache and do not use rate dependent compression

--
Darren Dunham                                           ddunham AT taos DOT com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >

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