This document explains how to circumvent a problem with slow performance on a server partition during the initialization of disks on client partitions.
Resolving The Problem
A behavior sometimes experienced by customers using an IBM i partition as the virtual I/O server for IBM i client partitions involves the high utilization of server partition resources while a client disk is being initialized to all zeroes, which is always initiated by an IBM i client partition when it adds the virtual disk to its disk configuration. The high utilization is especially undesirable when the server Network Storage Space which provides the backing storage for the client virtual disk is newly created and so already contains all zeroes, which makes the second initialization unnecessary. This double-initialization behavior is being eliminated in IBM i version 7.1 with PTF SI43969 and requisite PTFs MF53609 and MF53610.
After applying PTF SI43969 to the server, the initialization state of Network Storage Spaces linked to a Network Server Description (NWSD) of type *GUEST or *ISCSI will be maintained by the IBM i operating system. A newly created Network Storage Space will share its "all zeroes" state with the virtual I/O Licensed Internal Code, which will then manage the disk state based on I/O requests from the client. If the client requests that the disk be initialized to zeroes when the initialization state indicates it already contains all zeroes, the request will complete immediately and so avoid the unnecessary consumption of server resources to zero the disk a second time. Any write request from the client will change the disk to an uninitialized state which requires the disk storage to be zeroed again, if the client should subsequently request it. The initialization state is a permanent attribute of the Network Storage Space and so persists across such operations as varying off the NWSD, unlinking the storage space from the NWSD, saving and restoring the storage space, or duplicating the storage space (using the CRTNWSSTG command with the FROMNWSSTG keyword). Network Storage Spaces created on a previous version of IBM i or on version 7.1 without PTF SI43969 will be considered uninitialized, regardless of the contents of the storage space.
No modifications to client partitions are needed to take advantage of this change.
18 December 2019