Hi Ron, What happens to if our ficon card is 16gb, and fcp connection is 2gb, I try to do the simulation on monoplex lpar , the result is fine, now we are suspect the GRS or other system parm which will increase the disconnect time
Ron hawkins <[email protected]> 於 2018年2月 15日 星期四寫道： > Tommy, > > This should not be a surprise. The name "Synchronous Remote Copy" implies > the overhead that you are seeing, namely the time for the synchronous write > to the remote site. > > PPRC will more than double the response time of random writes because they > the Host write to cache has the additional time of controller latency, > round trip delay, and block transfer before the write is complete. On IBM > and HDS (not sure with EMC) the impact is greater for single blocks, as > chained sequential writes have some overlap between the host write, and the > synchronous write. > > Some things to check: > > 1) Buffer Credits on ISLs between the sites. If no ISLs then settings on > the storage host ports to cater for 30km B2B credits > 2) Channel speed step-down - If your FICON channels are 8Gb, and the FCP > connections are 2Gb, then PPRC writes will take up to four times longer to > transfer. It dep[ends on the block size. > 3) Unbalanced ISLs - ISLs do not automatically rebalance after one drops. > The more concurrent IO there is on an ISL, the longer the transfer time for > each PPRC write. There may be one opr more ISL that are not being used, > while others are overloaded > 4) Switch board connections not optimal - talk to your switch vendor > 5) Host adapter ports connections not optimal - talk to your storage vendor > 6) Sysplex tuning may identify IO that can convert from disk to Sysplex > caching. Not my expertise, but I'm sure there are some red books. > > There is good information on PPRC activity in the RMF Type 78 records. You > may want to do some analysis of these to see how transfer rates and PPRC > write response time correlate with your DASD disconnect time. > > Final Comment: do you really need synchronous remote copy? If your company > requires zero data loss, then you don't get this from synchronous > replication alone. You must use the Critical=Yes option which has it's own > set of risks and challenges. If you are not using GDPS and Hyperswap for > hot failover, then synchronous is not much better than asynchronous. > Rolling disasters, transaction roll back, and options that turn off > in-flight data set recovery can all see synchronous recovery time end up > with the same RPO as Asynchronous. > > Ron > > > > > > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of Tommy Tsui > Sent: Thursday, February 15, 2018 12:41 AM > To: [email protected] > Subject: Re: [IBM-MAIN] DASD problem > > Hi, > The distance is around 30km, do you know any settings on sysplex > environment such as GRS and JES2 checkpoint need to aware? > Direct DASD via San switch to Dr site , 2GBPS interface , we check with > vendor, they didn't find any problem on San switch or DASD, I suspect the > system settings > > Alan(GMAIL)Watthey <[email protected]> 於 2018年2月15日 星期四寫道： > > > Tommy, > > > > This sounds like the PPRC links might be a bit slow or there are not > > enough of them. > > > > What do you have? Direct DASD to DASD or via a single SAN switch or > > even cascaded? What settings (Gbps) are all the interfaces running at > > (you can ask the switch for the switch and RMF for the DASD)? > > > > What type of fibre are they? LX or SX? What kind of length are they? > > > > Any queueing? > > > > There are so many variables that can affect the latency. Are there > > any of the above that you can improve on? > > > > I can't remember what IBM recommends but 80% sounds a little high to me. > > They are only used for writes (not reads). > > > > Regards, > > Alan Watthey > > > > -----Original Message----- > > From: Tommy Tsui [mailto:[email protected]] > > Sent: 15 February 2018 12:15 am > > Subject: DASD problem > > > > > > > > Hi all, > > > > > > Our shop found the most job elapse time prolong due to pprc > > synchronization versus without pprc mode. It's almost 4 times faster > > if without pprc synchronization. Is there any parameters we need to > > tune on z/os or disk subsystem side? We found the % disk util in RMF > > report over 80, Any help will be appreciated. Many thanks > > > > ---------------------------------------------------------------------- > > For IBM-MAIN subscribe / signoff / archive access instructions, send > > email to [email protected] with the message: INFO IBM-MAIN > > > > ---------------------------------------------------------------------- > > For IBM-MAIN subscribe / signoff / archive access instructions, send > > email to [email protected] with the message: INFO IBM-MAIN > > > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, send email > to [email protected] with the message: INFO IBM-MAIN > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
