On 8 November 2012 00:58, Marcy Cortes <[email protected]> wrote: > The list is a little quiet so I thought I would ask this. > > It takes about 42 minutes here to dasdfmt a volume with 65519 cylinders on it. > It takes about 18 minutes to dd an already formatted volume over to a new one. > It also takes about 19 minutes to fill it up with zeros by cat /dev/zero to > it. > > Why does dasdfmt take so long? >
The full answer involves data and experiments and could at least excite the presenter for an hour ;-) (you can blame Marcy if you get trapped in there) On a real round brown disk, doing a "format write" is a delicate process that requires dedication and a steady hand. It's done one track at a time. This takes a full round trip per track, so roughly 1 million of those in your case. Given that, 20 would be explained. If there's more FICON things in between, there may be more hops to take and your I/O response might be worse. The amount of data does not look like it would saturate your NVS, but who knows what else is going on. If you upload an hour of data while this was running, I'd be most happy to investigate what is going on and whether there is room for improvement. Depending on where the bottleneck is, you could imagine to do PAV and a multi-threaded dasdfmt. We used to be able to tell dasdfmt to do just a range of cylinders (so you could run more in parallel) but that option was taken out because people forgot to format the entire disk When simply writing data (rather than format write) you can chain many tracks in a single I/O and need far less round trips and are down to the transfer rates. With high channel bandwidth that may indeed be faster. Most fun is to flashcopy a previously formatted pack. PS No, dasdfmt does not do a verify. There is a bit of reading afterwards, but that's it. ICKDSF however does do a verify. Rob ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
