life in the fast lane: zhyperlink · 2020. 11. 30. · • vsam reads ++apars • db2 log writes...
TRANSCRIPT
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Life in the fast lane: zHyperLinkJohn Baker
IntelliMagic
November 2020
Session 4AO
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IntelliMagic zAcademy Availability Intelligence
• Overview
• Traditional vs Synchronous I/O
• “Sync” in context
• Connectivity and DRP implications
• zHyperLink eligibility and real-world results
• Q&A
Agenda
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IntelliMagic zAcademy Availability Intelligence
Existing I/O components
3
CPU
IOP
Channels
FCD ports
Cache and NVS
HA’s and
ports
DA’s and
Drives
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IntelliMagic zAcademy Availability Intelligence
The life of an I/O (host side)
4
Open dataset via JCL andRead or write logical record
Builds channel program describingData location and type of access
May return immediately if in buffer
Handles priorities, queuing (IOSQ/PAV)and issues SSCH to engage
CSS hardware
SAP selects path to Disk Subsystem,Channel executes channel program
and handles data flow(Pend: CSS/CMR)
Application Program
Access Method
I/O Supervisor
Channel Subsystem
Disk Subsystem
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IntelliMagic zAcademy Availability Intelligence
The life of an I/O (DSS side)
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Disk Subsystem
Hard Disk/Flash Drives
Channel Subsystem - Decodes channel program (CKD/FB)- Manages cache and NVS- Manages extent integrity (Pend DB)- Initiates staging/destaging (Disc)- Manages RAID structures- Replication (Disc)
- Organized in Ranks/Pools/Arrays- Read/write data- Error checking
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IntelliMagic zAcademy Availability Intelligence
How long does all that take?
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IntelliMagic zAcademy Availability Intelligence
Synchronous I/O
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Application Program
Access Method
I/O Supervisor
PCIe zHyperLink
• Channel subsystem is bypassed
• CPU waits for PCI/DMA operation to complete; no task switching
• Processor cache content is preserved
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IntelliMagic zAcademy Availability Intelligence
Response vs Response
8
mic
roseconds
zHyperLink response
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IntelliMagic zAcademy Availability Intelligence
Sync Operation – Determined by z/OS
• Eligible I/Os are tried synchronously• CP spins waiting for sync I/O to complete• “Heritage” (traditional) I/O if cache miss – zHyperLink does not replace FICON
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IntelliMagic zAcademy Availability Intelligence
“Sync I/O” – Db2 vs zHyperLink
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Making the best of a bad situation:Turning a (bad) Db2 sync I/O into a (good) zHyperLink sync I/O
• Occurs when zHL eligible I/O experiences cache hit
• Reduces time required to complete I/O
• One 4K “block” (currently)
• Seek to maximize
zHyperLink sync I/O – GoodDb2 read sync I/O – Bad
• Occurs for data not loaded in advance by prefetch I/O
• Causes “costly” application wait times
• One 4K “page”
• Seek to minimize
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IntelliMagic zAcademy Availability Intelligence
Context: CF vs zHyperLink
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Familiarity with Coupling Facility concepts provides a great frameworkfor understanding zHyperLink processing
• Very fast: 20-30 mics
• CP spins during sync I/Os
• Safeguard from high CPU –cache misses re-driven as (async) FICON I/Os
zHyperLinkCoupling Facility
• Ultra-fast: 5-8 mics
• CP spins during sync reqs
• Safeguard from high CPU –heuristic algorithm “converts” subsequent requests to async
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IntelliMagic zAcademy Availability Intelligence
Connectivity – CEC to Storage
FICON links
At least 2 zHyperLinks
Maximum distance:150 meters
8 GB/sec optical links
DS8880Z14/15
zHyperLink is always Point-to-Point – no directors
zHyperLink is PCI link, not channel
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IntelliMagic zAcademy Availability Intelligence
No Metro Distance Mirrors
Common replication architecture for financial institutions
These synchronous distances not supported with zHyperLink
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IntelliMagic zAcademy Availability Intelligence
zHyperLink for Writes
To exploit zHyperLink for writes, synchronous copy must be local using zHyperWrite (prerequisite)
• Storage frame driven synchronous replication is not supported
• HyperSwap is supported (within 150m)
• Asynchronous copy is supported in combination with zHyperLink
Replication approach may need to be reevaluated
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IntelliMagic zAcademy Availability Intelligence
Potential Read-Only Approach
• IF zHyperLink exploitation is limited to reads, AND
• IF zHL-eligible reads all occur on DS8880 direct connected to CECs within 150m
• THEN current replication design may be viable; writes still occur through FICON
Primary:150 m
from CECs
Primary:150 m
from CECs
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© 2019 IBM Corporation
IBM Z – WSC Performance Team
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zHyperLink ™ Eligibility and Enablement– Eligibility designed to show potential benefit, even before zHyperLink™ Enablement
– Maintenance stream captures Eligibility, even if actual function disabled because of• Caller, Lack of Infrastructure, DFSMS Storage Class Granularity by default everything disabled (OA54822)
– Once zHyperLink enabled Eligibility may still be utilized• DFSMS Storage Class Granularity – by default everything “disable”
• Blocksize >4096
– Or Once zHyperLink enabled zHPF may still occur• Even “intra data set” with zHyperLink Enabled – E.g. Db2 Synchronous Reads and Prefetch Reads
• zHyperLink™ Read Misses (not a “Success”)
• Today, Writes
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Eligibility Callers
• Db2 v12 Sync Reads
• Db2 v11 Sync Reads
• VSAM Reads ++APARs
• Db2 Log Writes
Media Manager
Yes to all ?
• zHyperLink Infrastruture
• Caller Enabled
• DFSMS Enabled
• <=4096 Blocksize
If Not
zHyperLink Enabled - Attempts/Successes,
and Other SMF 42-6 zHyperLink Fields
• Db2 v12 Sync Reads
• Db2 v11 Sync Reads
• VSAM Reads ++APARs
• Db2 Log Writes
zHyperLink Eligible- Eligible / Read Hits
• Db2 v12 Sync Reads
• Db2 v11 Sync Reads
• VSAM Reads ++APARS
• Db2 Log Writes
zHPF – Normal SMF 42-6Non Eligible Callers
SMF 42-6 Fields
This slide courtesy of John Burg, IBM
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IntelliMagic zAcademy Availability Intelligence
Tracking eligibility and usage
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IntelliMagic zAcademy Availability Intelligence
VSAM: FICON and Synchronous Requests
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zHyperLinkResponse
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IntelliMagic zAcademy Availability Intelligence
Synchronous I/O Content (%)
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IntelliMagic zAcademy Availability Intelligence
zHL Enabled Storage Class“VSAM work”
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IntelliMagic zAcademy Availability Intelligence
Before and After: Linear Datasets (Db2)
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IntelliMagic zAcademy Availability Intelligence
Synchronous I/O ContentPercentage of all I/O
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IntelliMagic zAcademy Availability Intelligence
Detailed Stats from SMF 42
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IntelliMagic zAcademy Availability Intelligence
Eligible vs Active zHyperLink
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IntelliMagic zAcademy Availability Intelligence
LR vs SSCH and zHyperLink %
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IntelliMagic zAcademy Availability Intelligence
Weighted Response
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IntelliMagic zAcademy Availability Intelligence
DB2 Database: Activity and Response
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IntelliMagic zAcademy Availability Intelligence
DB2 Transaction Response Time
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IntelliMagic zAcademy Availability Intelligence
Database Sync I/O Waitms/commit
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IntelliMagic zAcademy Availability Intelligence
Summary: I/O is all relative!
Local Buffer
Coupling FacilityGroup Buffer Pool
zHyperLink Sync I/O
Storage System Enterprise HDD
FICON Cache Hit
Flash Back-end Miss
Average Tiered Back-end Miss
1 µs
8 µs
20 µs
150 µs / 0.15 ms
1 second
8 seconds
20 seconds
2.5 minutes
8.3 minutes
33.3 minutes
500 µs / 0.5 ms
2000 µs / 2 ms
By way of comparison … if local buffer access
took 1 second …
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IntelliMagic zAcademy Availability Intelligence
Sources
• D. Craddock et al. “zHyperLink: Low-latency I/O for Db2 on IBM Z and DS8880 storage”, IBM Journal of Research and Development. Vol 62, No. 2-3, Paper 13, March/May 2018. https://dl.acm.org/doi/10.1147/JRD.2018.2802070
• IntelliMagic White Paper: “zHyperLink: The Holy Grail of Mainframe I/O?”
• Frank Kyne, “Meet the Future of I/O – zHyperLinks”, Cheryl Watson’s Tuning Letter (CWTL) 2018 #2, pp. 86-116
• John Burg (IBM), “Assessing and Analyzing zHyperLink”. SHARE Pittsburgh, August 7, 2019, Session #25708.
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Please submit your session feedback!
• Do it online at http://conferences.gse.org.uk/2020/feedback/nn
• This session is 4AO
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GSE UK Conference 2020 Charity
• The GSE UK Region team hope that you find this presentation and others that follow useful and help to expand your knowledge of z Systems.
• Please consider showing your appreciation by kindly donating a small sum to our charity this year, NHS Charities Together. Follow the link below or scan the QR Code:
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