Simple layouts for ECKD and zfcp disk configurations on Linux on System z
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The document discusses performance evaluations of Linux disk configurations on System z, emphasizing various arrangements for ECKD, FCP, and SCSI disk access. It outlines the impact of single and multi-path configurations on input/output (I/O) operations and highlights the importance of using logical volumes and technologies like hyperPAV for optimal load balancing and throughput. Additionally, it addresses the administrative efforts needed for multipathing and the overall advantages of using striped logical volumes for better I/O performance.
Simple layouts for ECKD and zfcp disk configurations on Linux on System z
- 1. Simple layouts for ECKD and zfcp disk configurations on Linux on System z Thorsten Diehl Linux on System z System Evaluation thorsten.diehl@de.ibm.com 1 © 2011 IBM Corporation
- 2. Linux on System z Performance Evaluation FICON/ECKD dasd I/O to a single disk Assume that subchannel a corresponds to disk 2 in rank 1 Application program The full choice of host adapters can be used Only one I/O can be issued at a time through subchannel a VFS All other I/Os need to be queued in the dasd driver and in the block device layer until the subchannel is no longer busy with the preceding I/O DA ranks Block device layer Channel 1 subsystem Server 0 Page cache I/O scheduler a chpid 1 HBA 1 3 chpid 2 HBA 2 dasd driver Switch chpid 3 HBA 3 5 Server 1 chpid 4 HBA 4 7 2 Introduction to Linux features for disk I/O © 2011 IBM Corporation
- 3. Linux on System z Performance Evaluation FICON/ECKD dasd I/O to a single disk with HyperPAV VFS sees one device Application program The dasd driver sees the real device and all alias devices Load balancing with HyperPAV is done in the dasd driver. The aliases need only VFS to be added to Linux. The next slowdown is the fact that only one disk is used in the storage server. This implies the use of only one rank, one device adapter, one server DA ranks Block device layer Channel 1 subsystem Server 0 Page cache I/O scheduler a chpid 1 HBA 1 3 b chpid 2 HBA 2 dasd driver Switch c chpid 3 HBA 3 5 Server 1 d chpid 4 HBA 4 7 3 Introduction to Linux features for disk I/O © 2011 IBM Corporation
- 4. Linux on System z Performance Evaluation FICON/ECKD dasd I/O to a linear or striped logical volume VFS sees one device (logical volume) The device mapper sees the logical volume and the physical volumes Application program With a striped logical volume the I/Os can be well balanced over the entire storage server and overcome limitations from a single rank, a single device adapter or a VFS single server To ensure that I/O to one physical disk is not limited by one subchannel, PAV or HyperPAV should be used in combination with logical volumes LVM DA ranks dm Block device layer Channel 1 subsystem Server 0 Page cache I/O scheduler a chpid 1 HBA 1 3 b chpid 2 HBA 2 dasd driver Switch c chpid 3 HBA 3 5 Server 1 d chpid 4 HBA 4 7 4 Introduction to Linux features for disk I/O © 2011 IBM Corporation
- 5. Linux on System z Performance Evaluation FCP/SCSI LUN I/O to a single disk Assume that disk 3 in rank 8 is reachable via channel 6 and host bus adapter 6 Application program Up to 32 (default value) I/O requests can be sent out to disk 3 before the first completion is required The throughput will be limited by the rank and/or the device adapter VFS There is no high availability provided for the connection between the host and the storage server DA ranks Block device layer Server 0 Page cache 2 I/O scheduler chpid 5 HBA 5 chpid 6 HBA 6 4 SCSI driver Switch zFCP driver chpid 7 HBA 7 qdio driver Server 1 6 chpid 8 HBA 8 8 5 Introduction to Linux features for disk I/O © 2011 IBM Corporation
- 6. Linux on System z Performance Evaluation FCP/SCSI LUN I/O to a single disk with multipathing VFS sees one device Application program The device mapper sees the multibus or failover alternatives to the same disk Administrational effort is required to define all paths to one disk VFS Additional processor cycles are spent to do the mapping to the desired path for the disk in the device mapper Multipath DA ranks dm Block device layer Server 0 Page cache 2 I/O scheduler chpid 5 HBA 5 chpid 6 HBA 6 4 SCSI driver Switch zFCP driver chpid 7 HBA 7 qdio driver Server 1 6 chpid 8 HBA 8 8 6 Introduction to Linux features for disk I/O © 2011 IBM Corporation
- 7. Linux on System z Performance Evaluation FCP/SCSI LUN I/O to a linear or striped logical volume VFS sees one device (logical volume) Application program The device mapper sees the logical volume and the physical volumes With a striped logical volume the I/Os can be well balanced over the entire storage server and overcome limitations from a single rank, a single device adapter or a VFS single server To ensure high availability the logical volume should be used in combination LVM with multipathing DA ranks dm Block device layer Server 0 Page cache 2 I/O scheduler chpid 5 HBA 5 chpid 6 HBA 6 4 SCSI driver Switch zFCP driver chpid 7 HBA 7 qdio driver Server 1 6 chpid 8 HBA 8 8 7 Introduction to Linux features for disk I/O © 2011 IBM Corporation