To be honest I don't care about algorithm name.
However algorithms from 3490 and 3592 need not to be compatible, because
there is absolutely no possibility to use old cart in new drive and vice
versa. Yes, carts looks similar, but the drive won't accept wrong cart,
it will be rejected.
There is another story within Jaguar family. Here we have *limited*
compatibility. Limited, because i.e. TS1160 will not accept JA cart.
However TS1140 will read/write data written TS1130 on JB. Also TS1140
will read (no write) data on JB written in TS1120.
Whole compatibility matrix is quite complex, in fact it is
three-dimensional array (drive type, cart type, recording technology and
re-format ability as a bonus dimension).
Back to the topic: in every case where R/O or R/W is in effect there is
also support for compression. Compression is always on and transparent
to the user.
HTH
--
Radoslaw Skorupka
(looking for new job)
Lodz, Poland
W dniu 23.04.2021 o 03:54, (K.K.Paradox)T.Kobayashi pisze:
Thank you for all adivce.
I know the 3490 drive is the compression used by IDRC.
However, the 3592 appeared to have a different compressed algorithm.
So I asked if any 3592 drives is compatible.
See the bellow:
https://www.ibm.com/docs/en/ts3500-tape-library?topic=drives-3592-tape
Data compression
The 3592 tape drives use the data-compression method known as
streaming lossless data compression algorithm. The compression logic
for TS1120 and later tape drives operates at more than twice the
overall transfer rates of the 3592 J1A tape drive.
Best regards,
Toyokazu Kobayashi
----- Original Message ----- From: "Radoslaw Skorupka"
<[email protected]>
Newsgroups: bit.listserv.ibm-main
To: <[email protected]>
Sent: Friday, April 23, 2021 4:15 AM
Subject: Re: 3592 hardware compression
W dniu 22.04.2021 o 16:38, Ed Jaffe pisze:
On 4/22/2021 1:31 AM, (K.K.Paradox)T.Kobayashi wrote:
There is a tape where a DFDSS dump was created on a 3592 drive
(TS1130) with the COMPACT feature enabled.
Q1. Can I read this tape on another 3592 drive (such as TS1130 or
TS1140)?
Are the 3592 hardware compressions compatible?
IDRC is IDRC. At only about 3:1, It ain't great. But, it's
compatible...
Gentlemen,
Drive compression is *unpredictable* unless you know data to be written.
The true is same data on same drive will be compressed with same ratio.
BTDT. I spend a lot of time playing with compression ratios and
preparing data compressible 3:1, 6:1, 1:1, etc.
Long time ago I've got F37 abend, because my tape dataset exceeded
6TB - but it was on JA tape in J1A drive. Native capacity is 300GB,
so I got over 20:1. I don't know exact value, because RMM was unable
to record such big numbers - that was a reason of F37.
3:1 is marketing value, which is more or less based on typical data.
However "typical" is not well defined, and you may not know how much
typical is your dataset.
Remark:
We know marketing 3:1 value. There is another one: speed. Is your
drive capable to write 360MB/s? Great, but you actual throughput will
be lower. Nominal value is true for big blocksize *and* proper
compression ratio, usually nominal one.
Worse compression (i.e. 1:1) mean worse throughput, usually you will
get same compressed stream, so in case of 1:1 it would be 3 times worse.
Better compression ...can be even worse, much worse! Very good
compression means very little compressed stream. Tape drive can slow
down, there are several gears (speeds), but when the stream is not
enough to satisfy the lowest gear the data buffer is exhausted, drive
stops, rewinds a little and starts again. Veeeery slow.
Of course the above covers real tape drives only, so it is rather
historical.
--
Radoslaw Skorupka
(looking for new job)
Lodz, Poland
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [email protected] with the message: INFO IBM-MAIN
