General Sizing Discussion Jana Jamsek ATS Europe

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

IBM i specifics: Single-Level Storage

IBM i specifics: Handling Input Output operations

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

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

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

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

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

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

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

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

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

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.

Sector conversion