1. General Sizing Discussion Jana Jamsek ATS Europe

2. Typical Customers’ considerations
Daily workload
Interactive transaction workload
Requst: Short Transaction rensponse time
Batch job running during the night
Typically many jobs that run brief transactions with database operations
Copying of libraries
Saving to tape
Request: Duration of batch job within certain limits
Typical request: IBM i on External storage should perform as good as on internal disk

3. IBM i specifics: Single-Level Storage

4. IBM i specifics: Handling Input Output operations

5. Storage Manager – Handling IO operations
Storage management directories
Map disk and sector to a virtual address
Page tables
Internal disk
Pages
Virtual addresses
LUN on external storage

6. IO flow – Internal disk drives
Processors
IO flow
Main storage
MS bus - RIO
IO bus – PCI-X
Cache
Ex #5903, #5904
IOA
Ex SSF SAS disk drives
Internal Disk drives

7. IO flow –Natively connected external storage
Processors
IO flow
MS bus - RIO
Main storage
POWER
IBM i
IO bus – PCI-X
IOA
IOA
Ex #5735
SAN
HBA
HBA
Processor,
cache
Processor,
cache
PCI-e
Storage
System DA DA FC
DDM
LUN
Note: the connections in External storage show DS8000

8. IO flow – Storage system connected with VIOS
Request
IBM i client sends a request to read data from disk. The request (SCSI command) proceedes
through the virtual SCSI adapter in IBM i client, the virtual SCSI adapter in VIOS, and by AIX
code to the device driver of a physical FC adapter in VIOS. The FC adapter then
communicates a request to external storage. The requested block of data is transferred from
the Storage System to th eFC adapter in VIOS. VIOS and Hypervisor then communicate to
transfer the data to main memory in IBM i client through Power6 hardware, such as multi
adapter bridge, RIO-G, and memory buffer. Acknowledgement about successful transfer goes
the same way as the request, but in the opposite direction—through the adapter in VIOS, the
device driver in VIOS, it is proceeded by AIX code to the virtual SCSI adapter in VIOS, the
virtual SCSI adapter in IBM i, and further to IBM i storage management.
Power Hadrware
Data
Storage system

9. IO flow - virtualization with SVC
IBM i client
POWER
VSCSI
VIOS
VIOS
SVC
vdisk
Background storage system
Physical disk drives
mdisk

10. Why is the number of LUNs important
SCSI command tag queuing allows 6 concurrent IO operaitons to a LUN
Available with IOP-less adapters
The more LUNs the more concurrent operations to disk storage
In VIOS, the queue depth for IBM i volume is 32
The more LUNs are defined, the more Storage management server tasks are used, consequently better IO performance

11. Why is the number of disk drives (DDMs) important
Each LUN spans multiple disk drives (DDMs)
The same set of DDMs is used by multiple LUNs
The more physical disk drives (disk amrs) are available and the higher is their rotation, the faster are IO on each LUN
RAID level of DDMs usually influeneces performance too
Example:
LUNs in DS8000
With Rotate extents
method

12. Why is Multipath important
All path to external storage are used for IO operations
IOs are done in Round Robin accross all path
Exception is DS5000 where one path through preferred controller is active and all the other path is passive

13. Why is cache important Read operations:
A directory lookup is performed if the requested track is in cache. If the requested track is not found in the cache, the corresponding disk track is staged to cache. The setup of the address translation is performed to map the cache image to the host adapter, the data is then transferred from cache to host adapter and rther to the host connection.
The more data are red from cache the faster is read response time

14. Why is cache important Write operations:
Every write operaiton is done to cache
A directory lookup is performed if the requested track is in cache. If the requested track is not in cache, segments in the write cache are allocated for the track image. The data is then transferred from the host adapter memory to the two redundant write cache instances.
Data are destaged to disk with certain frequency by cache algorythm
Frequent destages cause a certain delay in write operations to cache
Write cache overflow: need to destage data in order to be able to allocate a track in the cache to be written to
Write cache efficiency: The Write Efficiency is a number representing the number of times a track is written to before being destaged to disk. 0% means a destage is assumed for every single write operation, a value of 50% means a destage occurs after the track has been written to twice.

15. Sector conversion