IBM(R) Multipath Subsystem Device Driver Version 1.6.0.1-2 README for Linux ------------------------------------------------------------------------------- CONTENTS 1.0 About this README file 1.1 Who should read this README file 1.2 How to get help 2.0 Prerequisites for SDD 2.1 Supported HBA Driver Levels 2.2 Supported Filesystems 3.0 SDD Change History 3.1 Defects Fixed 3.1.1 Common 3.1.2 ESS/DS8000/DS6000 Defects 3.1.3 SVC Defects 3.1.4 SVCCISCO Defects 3.2 New Features 3.3 Feature Details 3.4 Known Issues 3.5 Correction to User's Guide 4.0 User License Agreement for IBM Device Drivers 5.0 Notices 6.0 Trademarks and Service Marks ------------------------------------------------------------------------------- 1.0 About this README file Welcome to IBM Totalstorage Multipath Subsystem Device Driver (SDD). This README file contains the most recent information about the IBM Totalstorage Multipath Subsystem Device Driver, Version 1.6.0.1-2 for Linux. IBM recommends that you go to the following Web site to get the most current information about this release of SDD: http://www.ibm.com/servers/storage/support/software/sdd.html You should carefully review the following information available through the website: 1. The most current README file. This will contain corrections to this readme file, corrections to the SDD User's Guide, and other documentation updates discovered since this copy of the README was prepared. 2. The Multipath SDD User's Guide. Because SDD can be installed in so many different environments / configurations, detailed information about each environment is placed in the appropriate chapter of the Multipath SDD Users Guide. The 'Summary of Changes' section of the SDD Users' Guide can help you quickly determine if the latest changes affect you. 3. The Flashes. As we become aware of any information that is likely to impact a broad set of our customers, Flashes are prepared and posted on this site. You should review this section periodocally to see any new Flashes that have been posted since your last review. For prerequisites information, be sure to look in the Multipath SDD User's Guide as well as the prerequisites section of this readme file for the latest updates. 1.1 Who should read this README file This README file is intended for storage administrators, system programmers, and performance and capacity analysts. The information in this file only applies to customers who run: 1. ESS, DS8000, DS6000, SAN Volume Controller, or SAN Volume Controller for Cisco MDS 9000 2. ESS and SAN Volume Controller 3. ESS and SAN Volume Controller for Cisco MDS 9000 1.2 How to get help Go to the following Web site for SDD technical support and for the most current SDD documentation and support information: http://www.ibm.com/servers/storage/support/software/sdd.html Go to the following Web site for the IBM ESS Open Systems support: http://www.storage.ibm.com/hardsoft/products/ess/supserver.htm Go to the following Web site for IBM TotalStorage DS8000 support: http://www.ibm.com/servers/storage/disk/ds8000/index.html Go to the following Web site for IBM TotalStorage DS6000 support: http://www.ibm.com/servers/storage/disk/ds6000/index.html Go to the following Web site for IBM TotalStorage SAN Volume Controller support: http://www.ibm.com/servers/storage/support/virtual/2145.html Go to the following Web site for IBM TotalStorage SAN Volume Controller for Cisco MDS 9000 support: http://www.ibm.com/servers/storage/support/virtual/2062-2300.html Call one of the following numbers to obtain nontechnical or administrative support, such as hardware and software orders, hardware maintenance, services contract of entitlement, and invoices: .For commercial or state and local support operations: 1-877-426-6006 (Listen to the voice prompts) .For business partner support operations: 1-800-426-9990 .For federal government support operations: 1-800-333-6705 ------------------------------------------------------------------------------- 2.0 Prerequisites for SDD One of the following combinations of linux distribution and associated vendor compiled binary kernel packages: SuSE SLES 9 (x86) with one of the following kernels: kernel-smp-2.6.5-7.139 ^ kernel-bigsmp-2.6.5-7.139 ^ kernel-smp-2.6.5-7.145 ^ kernel-bigsmp-2.6.5-7.145 ^ SuSE SLES 9 (ppc64) with one of the following kernels: kernel-pseries64-2.6.5-7.139 ^ kernel-pseries64-2.6.5-7.145 ^ * Not officially supported in this release. ^ Newly supported in this release. =============================================================================== 2.1 Supported HBA Driver Levels Intel (x86) o Qlogic qla2x00 8.00.00 pSeries (ppc64) o Emulex lpfc 2.10g =============================================================================== 2.2 Supported Filesystems o ext3 o reiserfs o xfs ------------------------------------------------------------------------------- 3.0 SDD Change History 1.6.0.1-2 o Add support for SuSE SLES 9 SP1 (Linux 2.6 kernel) =============================================================================== 3.1 Defects Fixed 3.1.1 Common 1.6.0.1-2 o PCR 2447 Add support for SuSE SLES 9 (Linux 2.6 kernel) 3.1.2 ESS defects None 3.1.3 SVC defects None 3.1.4 SVCCISCO defects None =============================================================================== 3.2 New Features 1.6.0.1-2 o Support for SuSE SLES9 SP1 (Linux 2.6 kernel) =============================================================================== 3.3 Feature Details o Initial support for SuSE Linux Enterprise Server (SLES) 9 SP1 running on the Linux 2.6 kernel. Note that the Linux 2.6 kernel is significantly changed from the Linux 2.4 kernel supported on our previous releases. This release is only for ESS storage. o New kernels are supported in this release. Please see the list of supported kernels listed at the start of this document. =============================================================================== 3.4 Known Issues o SAN Fabric Configuration and Maintenance Limitations A number of maintenance operations in SAN fabrics have been observed to occasionally cause I/O errors for Linux hosts. To avoid these errors, I/O on Linux hosts must be quiesced prior to doing any type of SAN re-configuration activity, switch maintenance or storage maintenance. During Concurrent Code Load (CCL), I/O errors have been occasionally observed. All I/O must be quiesced on these systems before CCL is started and must not be restarted until the code load is complete. All host paths must be online, and the fabric must be fully redundant with no failed paths. o Module loading at boot time When installing with supported fibre-channel Host Bus Adapters (HBAs), SLES 9 will load the fibre-channel adapter driver earlier in the OS boot-up order than the internal SCSI adapter card driver. This may cause problems because the internal disks are usually referenced using a static device entry (such as "/dev/sda3") in the /etc/fstab entry for the OS to load the root filesystem disk. The loading of the HBA driver could cause a disk on the SAN (such as from an ESS) to be loaded as "/dev/sda" and the real local root disk to be moved to something like "/dev/sdb". This static naming convention could cause your system to crash at boot time. One workaround is to reorder the entries in the configuration file /etc/sysconfig/kernel. This file indicates the order in which the drivers are loaded in the initial ramdisk image Linux uses in order to boot (called the initrd). The INITRD_MODULES parameter determines the driver load order at boot time. You might have something that looks like this: INITRD_MODULES="lpfcdd sym53c8xxi" where "lpfcdd" is the Emulex HBA driver and "sym53c8xxi" is the internal SCSI driver. You would want to place the lpfcdd entry after the internal SCSI driver entry, such as this: INITRD_MODULES="sym53c8xxi lpfcdd" After you change this entry, run the command "mkinitrd." This will create a new initial ramdisk image with the driver load order changed. Next time you reboot the system, the new order will go into effect. If you have configured your SAN LUNs already and the system is currently crashing at boot time (i.e. you are seeing the symptom above), you can unplug the cables from the HBA to get the system to boot up normally. Then, follow the above steps to change the driver load order and plug the cables back in during the next reboot. o LVM2 with SDD LVM2 refers to a new userspace toolset that provides logical volume management facilities on Linux. For more information about LVM2, see the LVM2 website at http://sources.redhat.com/lvm2/ or run "man lvm". In order for LVM2 to work on your machine, you must have the LVM2 rpm installed; look on the OS install CD's for the LVM2 package. In order to get LVM2 to run with SDD, several changes must be made to the LVM configuration file /etc/lvm/lvm.conf. In this file, there are several fields that must be modified. As always, back up the file before attempting to modify it. Under the section "devices", there are two values that must be modified. The first value is "filter". In the file, you might see the default as the following: # By default we accept every block device except udev names: filter = [ "r|/dev/.*/by-path/.*|", "r|/dev/.*/by-id/.*|", "a/.*/" ] This filter is too broad for SDD, because it will recognize both SDD vpath devices as well as the underlying paths (i.e. /dev/sdxxx) to that SDD vpath device. We want to narrow this regular expression to just accept vpath devices, and not the underlying scsi disk devices. The easiest way to do this is to modify the regular expression to just accept the name "vpath", and to ignore all other types of devices. Of course, this is the simplest example; your environment might be slightly different, but you can adjust the example accordingly: filter = [ "a/vpath[a-z]*/", "r/.*/" ] This regular expression will accept all vpath devices and reject all other devices under /dev. Another value that you need to change is "types". In the file, you will see that it is commented out: # List of pairs of additional acceptable block device types found # in /proc/devices with maximum (non-zero) number of partitions. # types = [ "fd", 16 ] You want to delete the comment marker, and replace "fd" with "vpath". This allows LVM to add vpath to its list of internally recognized devices. The partition number should stay at 16. For example: types = [ "vpath", 16 ] After making these two changes, save the lvm.conf file. Now, you should be able to run "pvcreate" on vpath devices (i.e. /dev/vpatha) and create volume groups using "vgcreate". o Timeouts with Qlogic qla2x00 8.00.00 Storage Adapter The Qlogic 8.00.00 driver enforces an I/O queue depth limit per path, not per LUN. This value is controlled through Qlogic's ql2xmaxqdepth parameter. Since the Qlogic driver does not enforce a queue depth limit per LUN, multiplying the number of paths to a LUN will also multiply the maximum queue depth per LUN. For example, using SDD with 4 paths to a LUN and a queue depth of 32 will allow up to 32 x 4 = 128 I/O requests to be queued to the LUN at an any instant in time. Thus, using SDD with the Qlogic driver can significantly multiply the I/O load to a LUN versus what is normally generated using a single-pathed solution. In some scenarios, heavy I/O load may cause many I/O requests to timeout because the ESS storage is overloaded with I/O requests and is taking longer to respond. Typically, this is indicated through a series of SCSI errors with a 0x20000 return code. For example, you may see a series of error messages for different paths in /var/log/messages that resemble: kernel: SCSI error : <7 0 0 4> return code = 0x20000 In addition, having saturated queues is another clue that indicates your storage is overloaded. The queues are saturated if the "Pending reqs" queue depth values listed in the "SCSI LUN Information" section of /proc/scsi/qla2xxx/[port_number] are close to or equal to the queue depth limit. For example, a part of an entry for a full path queue may look like this, assuming a queue depth limit of 32 is being used: SCSI LUN Information: (Id:Lun) * - indicates lun is not registered with the OS. ( 0: 4): Total reqs 1817, Pending reqs 32, flags 0x0, 0:0:84 00 ( 0: 5): Total reqs 2555, Pending reqs 32, flags 0x0, 0:0:81 00 ( 0: 6): Total reqs 3003, Pending reqs 32, flags 0x0, 0:0:81 00 ( 0: 7): Total reqs 1971, Pending reqs 32, flags 0x0, 0:0:81 00 Consequently, to avoid overloading a LUN, you can manually enforce a queue depth limit per LUN by adjusting the Qlogic driver's queue depth limit, i.e. the ql2xmaxqdepth parameter. This should be set to the desired per LUN queue depth divided by the number of paths to the LUN. For example, using SDD with 4 paths to the LUN and the Qlogic ql2xmaxqdepth value of 32 as the desired value, the new Qlogic queue depth limit would be set to 32 / 4 = 8. Note, that the appropriate queue depth is not only determined by the number of paths to each LUN, but the number of LUNS per host and the number of hosts connected to the storage should also be considered. You can adjust the queue depth limit by reloading the Qlogic qla2xxx driver with the ql2xmaxqdepth parameter specified. One method is to specify ql2xmaxqdepth at the command line when loading the qla2xxx driver: modprobe qla2xxx ql2xmaxqdepth=[new_queue_depth] The other method is to add the line: options qla2xxx ql2xmaxqdepth=[new_queue_depth] in /etc/modprobe.conf, before reloading the driver with modprobe. =============================================================================== 3.5 Correction to User's Guide None ------------------------------------------------------------------------------ 4.0 User license agreement for IBM device drivers See LICENSE file included in package (in /opt/IBMsdd) ------------------------------------------------------------------------------- 5.0 Notices This information was developed for products and services offered in the U.S.A. IBM may not offer the products, services,or features discussed in this document in other countries. Consult your local IBM representative for information on the products and services currently available in your area. 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