May 4, 2016

dasdfmt performance

This week I got asked multiple times on how to speed up the formatting of classical ECKD DASDs. The command to use is dasdfmt which is part of the s390-tools package. In the newer distributions there is an option called --requestsize=..... which allows to specify the number of cylinders to use in each format step. Basically it's the amount of parallelism that should be used.
The drawback is that on classical ECKD devices you can only have one outstanding IO. So to take advantage of this you need (Hyper)PAV installed and enabled for the DASD you want to format. For the comparison here I used one base device and 16 aliases and a 3390 mod 9 DASD with 10017 cylinders. Varying the requestsize from 1 to 16 on Ubuntu 16.04 I got the following throughput:


As you can see you can get a decent speedup. You can get well under 10s in my example. So give it a try. 

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