Bill > > Based on everything I have read lately, I now believe it is possible to > start 256 I/O requests from one LPAR to the > same device before the first one ends if that device is in an ESS LCU > with > four FICON channels between that > LCU and the LPAR that does the I/Os, if that LPAR has the device > defined as > a PAV base device with 255 alias > devices in the same LCU, and if all four FICON channels are in the > base > device's UCB channel path matrix.
That's only if you are connected to a z9. The z990, z900 and G6 have less OE per channel so you need 8 channels to get 256 IO. There can be no other IO to any other LCU daisy chained on the same channel(s). The OE supported by the storage port must also not be exhausted due to fan-in of multiple channels. In a simple model of 4xchannels dedicated to one LCU with one base and 255 alias you are correct. > These I/Os will appear to be simultaneous, but at any given instant, > no more > than 64 of the 256 will be actively > transferring data to or from the LCU. The other 192 will be > disconnected > for various reasons. Not true. There is no disconnect on FICON. The channel is moving frames or not. The number of OE with data or command in a frame on the channel will depend on how the particular server and storage models handle interleaving. This is a theoretical > maximum and not necessarily a practical limit. If eight ESCON > channels are > the link between the device and the > ESS LCU, then the number of simultaneously startable I/Os to the device > will > be more than eight but smaller than 256. In tests with zero cache hits I've seen channels with average 47 OE - an average meaning there are times when there were larger and smaller numbers. That's with 1024 spindles and 64x4Gb channels. > > Is all of this correct? > > I have been away from the bleeding edge too long. :-( I think the discussion may be accidentally creating confusion about OE and channel limitations at a single device level. The number of OE on a channel is the sum of all IO on the channel no matter how many volumes and LCU are sharing it. Ron ---------------------------------------------------------------------- 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
