John, Cache Fast Write reduces cache utilisation in HDS and IBM controllers.
In HDS a normal write has a second copy in Global cache until it is destaged to disk. With Cache Fast write there is only one copy in cache so cache usage is halved for those writes waiting to be destaged to disk. For IBM you save NVS usage. A Cache Fast Write is written to cache, but no copy is written to the NVS. Because of the NVS path overheads in E20, F20 and ESS you will get better throughput with CFW on in a box running between 300-600MB/sec. For EMC DMX and Symmetrix they don't mirror anything in cache so CFW doesn't save you anything. For DMX3 they mirror everything - reads and writes - so CFW doesn't save you anything there either. DFSORT does build some honking great long IO chains when CFW is on, which my gut feeling says is more efficient then lotsa SSCH. O haven't seen the same behaviour with Syncsort. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of John (IBM-MAIN) > Sent: Friday, 24 February 2006 12:59 AM > To: IBM-MAIN@BAMA.UA.EDU > Subject: Re: CFW and DFSORT > > > Hi all > > because of GDPS Hyperswap-Tests we want to disable Cache Fast Write. We > > were wondering which jobs would be affected by this change and we found > > out that DFSORT has an option CFW=Y, which is our default. > > 1. how will DFSORT react if option CFW=Y is used and on the HW it is > > disabled ? > > 2. Is this feature actually still used by DFSORT ? I am asking because > > CFW rate is 0.1 in our RMF report. > > I can't answer for DFSORT, but we had no problem with Syncsort with > turning off CFW. > (If the software is smart - it would check the hardware status first!) > > The same restrictions appear for Concurrent copy. > > John. > > ---------------------------------------------------------------------- > 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 ---------------------------------------------------------------------- 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
