Pardon my bringing back an old thread, but - I wanted to see how much better is the COMPRESS option over the HWCOMPRESS in regards to CPU time and was pretty surprised when my results suggested that HWCOMPRESS is persistently more efficient (both CPU and channel utilization -wise) than COMPRESS:
DFDSS DUMP with OPT(4) of a VSAM basic format to disk (basic format): STEPNAME PROCSTEP RC EXCP CONN TCB SRB CLOCK DUMP-HWCOMPRESS 00 14514 93575 .25 .07 2.3 output was 958 cyls. DUMP-COMPRESS 00 14819 92326 .53 .07 2.5 output was 978 cyls. DUMP-NOCOMP 00 15283 103K .13 .08 2.4 output was 1,017 cyls. DFDSS DUMP with OPT(4) of a PS basic format to disk (basic format): STEPNAME PROCSTEP RC EXCP CONN TCB SRB CLOCK DUMP-HWCOMPRESS 00 13317 154K .44 .19 6.2 output was 877 cyls. DUMP-COMPRESS 00 14692 157K .68 .19 5.1 output was 969 cyls. DUMP-NOCOMP 00 35827 238K .14 .21 7.9 output was 2,363 cyls. Running on a 2098-I04. DFSMSDSS V1R09.0. So, how come I get different results than the original poster? The test data was database-type data sets.. Best Regards, Yifat -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Andrew N Wilt Sent: Friday, December 03, 2010 1:45 AM To: [email protected] Subject: Re: Hardware-assisted compression: not CPU-efficient? Ron, Thank you for the good response. It is true that the DFSMSdss COMPRESS keyword and HWCOMPRESS keyword do not perform the same types of compression. Like Ron said, the COMPRESS keyword is using a Huffman encoding technique, and works amazing for repeated bytes (just the types of things you see on system volumes). The HWCOMPRESS keyword utilizes a dictionary based method, and works well, supposedly, on customer type data. The CPU utilization of the HWCOMPRESS (dictionary based) is indeed larger due to what it is doing. So you should choose the type of compression that suits your CPU utilization needs and data type. It was mentioned elsewhere in this thread about using the Tape Hardware compaction. If you have it available, that's what I would go for. The main intent of the HWCOMPRESS keyword was to provide the dictionary based compression for the cases where you were using the software encryption, and thus couldn't utilize the compaction of the tape device. Thanks, Andrew Wilt IBM DFSMSdss Architecture/Development Tucson, Arizona ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
