Episode 20 “Two Is One And One Is None”

Here are the show notes for Episode 20 “Two Is One And One Is None”. The show is called this because our Topics topic is trying to figure out how to archive family photos and videos.

Where We’ve Been Lately

Marna’s been to Z Tech U – Hollywood Florida. Great conference!

Feedback

We’ve received feedback that the stereo too aggressive. This episode has it narrowed, with a different audio tool.

What’s New

  • Dynamic IODF activation for Standalone CFs (before needed a POR, now can be driven remotely from another CEC)
    • Z14 GA2 for both driving and target, PR/SM-based solution which needs one more POR on target to establish a firmware-defined Master Control Services LPAR
    • Need some z/OS APARs: HCM-IO25603, IOS-OA53952, HCD-OA54912, IOCP-OA55404
  • Asynchronous Cache Structure XI. Is also with Z14 GA2, and there is expected to be Db2 support PTFs.

Mainframe: zFS Shrink, Only in z/OS V2.3

  • Top customer requirement. A system command for reducing the size of a zfs file system. Not be confused with compressing files within a file system.
  • You specify a target size with the size option, gives final size in KB, gets rounded to 8K boundary
    • -noai option: means no active increase. A file system is being accessed, might need additional blocks over the shrink size given. so it can be “actively increased” by default.
      • If you need to actively increase to the original size of the file system, the shrink command ends with error.
      • If you don’t want to active increase (-noai) and you need to actively increase, ends with error.
  • During a shrink a scan occurs to determine what blocks must move…longest part of the operation. Blocks are moving from the portion to be released, into the portion that is to remain.
    • After Blocks are moved, and then space is release – in which it will be briefly quiesced. Applications do not need to be stopped when doing a shrink.
    • It is recommended not to shrink during peak times you need the files.
  • To know how big to make the file after the shrinkg, use zfsadm fsinfo for aggregate size (in K), free size in (8k blocks), and 1k fragments.
    • Even better hint! Use df -kP to see 1k used and available, and those sizes are consistent for shrink.
  • Nothing right now to help with suggesting a size.
    • Don’t pick a final size that is too small, so you keep have to growing.
  • Reminder to use aggrgrow and zfsadm grow increase the size of the filesystem.
  • Monitor with SMF 92 subtype 50, for both grow and shrink events. Subtype 59 for # of I/Os and rate, but might occur too often, so use it wisely.

Performance: CPENABLE and HiperDispatch

Each I/O ends with an Interrupt, which needs to be handled by a processor, and needs to be handled in a timely way. When an I/O interrupt is handled the processor handling it issues aTest Pending Interrupt (TPI) instruction. If this test returns “true” this processor handles the (detected) pending interrupt. If “false” then the processor has no more interrupts to handle – for the time being.

If many of these TPI tests result in “true” it suggests a queue has built up – which might indicate temporarily enabling more processors to handle interrupts.

There’s a trade off between timeliness and processor efficiency. The CPENABLE parameter’s values manage this trade off. There are two values: if TPI% below first disable a processor from handling I/O interrupts, and if TPI% above second enable a processor to handle them.

Without Hiperdispatch, access to CPU is smeared across online processors, as the LPAR’s weight is evenly spread across its logical processors. Without Hiperdispatch it is recommended that CPENABLE be set to 0,0 which allows all processors to handle interrupts.

With Hiperdispatch, however, access to CPU is corralled into fewer processors – with the weight not being spread evenly across the LPAR’s logical processors: A Vertical High (VH) logical processor has a “full engine” weight; The remaining weight is spread across 0 or 1 or 2 Vertical Medium (VM) logical processors. Vertical low (VL) logical processor have zero weight.

With Hiperdispatch it is recommended to set CPENABLE to 10,30. This corrals interrupt handling into fewer processors much of the time. It’s in the spirit of the weight distribution.

In terms of instrumentation, SMF Type 70 is useful:

  • It documents LPAR Setup, including HiperDispatch State, logical Engines and weights, and Verticals / Horizontals.
  • It counts Interrupts & TPIs, enabling you to calculate the TPI Percentage, down to the logical processor level.

In a recent customer Data Sample there were a couple of different types of LPARs:

  • Some with Hiperdispatch enabled – with CPENABLE of 10,30 – where the logical processors were enabled from 0 upwards to handle I/O interrupts.
  • Some without Hiperdispatch enabled – with CPENABLE of 0,30 – where the logical processors were enabled from the highest downwards to handle I/O interrupts.
  • It probably would’ve shown smearing of I/O interrupt handling across all the logical processors with a CPENABLE value of 0,0 – but this is conjecture.
  • It showed LPARs with tiny weights: 0.1 engines’ of weight on a 2,3,4,5 way which is not going to be that timely in servicing I/O interrupts.

Overall this topic shows I/O Interrupt Enablement is a topic worthy of consideration to get timeliness vs efficiency right – particularly in the Hiperdispatch era. Also that the instrumentation really helps.

Topics: Archived Family Information

  • Talking about personal and family information: photos, audio, and video only. Not writings.
  • Backing up: Two Is One And One Is None. Need multiple backup techniques at different physical locations. Multiple cloud locations?
  • Modern media vs legacy: when to adopt new technology and how to convert?
  • Google Photos Retrieval
  • Apple Photos app
  • Finder search inside files is used to find outline elements from previous shows.
  • Some serious questions:
    • “What happens when I’m dead?” Facebook, for one, has a protocol. Google has a protocol.
    • Ideally write a will and tell family how to handle material.
    • Will anyone else care about the material?
    • “What about Big Brother” : Everyone has something to hide, it’s about trusting the service provider
    • “Who owns the material?” and do you care?

Customer requirements

  • z/OSMF Workflow “Deep” Search 126042
    • Within a z/OSMF Workflow instance, allow the user to look for an argument within the workflow itself. Right now, the search function only finds strings that are in the titles of the steps, and not in the “tabs” on the insides (such as general, instructions, notes, …).
    • What about find and replace? Not sure you want to replace something that is in the instance. Workflow designing isn’t in this scope.

Places we expect to be speaking at

  • Whittlebury Hall, Nov 5-7, 2018 GSE UK Huge attendance already registered!

On the blog

Contacting Us

You can reach Marna on Twitter as mwalle and by email.

You can reach Martin on Twitter as martinpacker and by email.

Or you can leave a comment below. So it goes…

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