Tim, The main reason to block the TMC is space utilization. If you are currently allocated as 340 X 340 and you change to the recommended 340 X 8840 you will end up using only about 1/3 the amount of dasd.
The reason that 8840 was chosen was that it gives well over 90% utilization on the DASD track; yet doesn't require a huge amount of ECSA to be reserved. Also, for direct I/O (read a single record, write a single record) we have to read and write a block at each time. So, to read a 340-byte record requires a read of either 8840 bytes of 27880 bytes. Granted, the majority of I/O time is spent on connecting to the device versus actually transferring the data; but still do you really want to xfer 27880 bytes every time you want to read or write a single record. We do have some clients runing with 27880 and they report no problems. So, the choice is yours. But for space utilization, 8840 is "close" to optimum but only requires a total of 26,520 bytes of ECSA versus 83,640 bytes. Strictly your choice, but the only reason for blocking the TMC is improved space utilization and 8840 will give you a three-fold improvement. Russell Witt CA-1 Level-2 Support Manager -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] Behalf Of Hare, Tim Sent: Monday, August 20, 2007 3:14 PM To: [email protected] Subject: CA-1 TMC Reblock - recommended size? I am at long last getting around to reblocking my TMC.. the TMSBLDVR utility gives space calculations for block size 8840; but of course that's not the only size possible. Is there any particular reason to use 8840 (26 records per block)? Is there a negative performance or availability impact from using 27880 (72 records per block instead of 26)? What sizes are being used by other CA-1 shops? Tim Hare Senior Systems Programmer Florida Department of Transportation Tel: +1 (850) 414-4209 ---------------------------------------------------------------------- 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
