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V4.2.x - IBM System Storage SAN Volume Controller Restrictions
 Preventive Service Planning
 
Abstract
This document lists the restrictions specific to SAN Volume Controller V4.2.x. There may be additional restrictions imposed on hardware attached to SAN Volume Controller e.g. switches and storage etc.
 
Content

DS4000 Maintenance
Host Limitations
SAN Fibre Networks
SAN Routers and Fibre Channel Extenders
SAN Maintenance
SAN Volume Controller Concurrent Code Load CCL
Maximum Configurations



DS4000 Maintenance

SVC supports concurrent ESM firmware upgrades for those DS4000 models listed as such on the "Supported Hardware List" when they are running either 06.23.05.00 or later controller firmware. However, controllers running firmware levels earlier than 06.23.05.00 will not be supported for concurrent ESM upgrades. Customers in this situation, who wish to gain support for concurrent ESM upgrades, will need to first upgrade the DS4000 controller firmware level to 06.23.05.00. This action is a controller firmware upgrade, not an ESM upgrade and concurrent controller firmware upgrades are already supported in conjunction with SVC. Once the controller firmware is at 06.23.05.00 or later the ESM firmware can be upgraded concurrently.

Note: The ESM firmware upgrade must be done on one disk expansion enclosure at a time. A 10 minute delay from when one enclosure is upgraded to the start of the upgrade of another enclosure is required. Confirm via the Storage Manager application's "Recovery Guru" that the DS4000 status is in an optimal state before upgrading the next enclosure. If it is not, then do not continue ESM firmware upgrades until the problem is resolved.



Host Limitations

Windows SAN Boot Clusters (MSCS):

It is possible to SAN Boot a Microsoft Cluster subject to the following restrictions imposed by Microsoft:
  • Windows 2000 Server clusters require that the boot disk be on a different storage bus to the cluster server disks.
  • On Windows 2003, clustered disks and boot disks can be presented on the same storage bus, but ONLY if the Storport driver is being used.

These restrictions and more are described in the Microsoft White Paper: "Microsoft Windows Clustering: Storage Area Networks".

We have not tested, and therefore do not support, modifying the registry key as suggested on page 28 (which would allow boot disks and clustered disks on the same storage bus on Windows 2003 without the Storport driver).


Oracle RAC 10g:

1. ASM disks cannot be removed/deleted without bringing down the Oracle ASM instance.
2. ASM cannot recognize the size change of the disk when SVC disk is resized unless the disk is removed from ASM and included again.
3. For RHEL4 set Oracle Clusterware 'misscount' parameter to a bigger one to allow SDD to do path failover first. The default miscount setting 60s is too short for SDD. We recommend to set it 90s or 120s.
Command to use: crsctl set css misscount 90


SLES10 Series Z:

The FC transport class keeps all outstanding I/O for a certain time (timeout value: default are 60 sec) until it decides that the remote port will note come back. This causes a temporary i/o stall in case of FC link incidents or when paths are varied offline. The timeout value can be set for each remote port via sysfs: /sys/class/fc_remote_ports/rport-0:0-0/dev_loss_tmoAlternatively this value can be preset for all remote ports at module load time of the scsi_transport_fc module via the dev_loss_tmo parameter.



SAN Fibre Networks

Please refer to this document for details on how to configure a supported SAN:

IBM System Storage SAN Volume Controller V4.2.1 - Software Installation and Configuration Guide



SAN Routers and Fibre Channel Extenders

Fibre Channel Extender Technologies:

IBM will support any fibre channel extender technology provided that it is planned, installed and tested to meet the requirements specified in:

IBM System Storage SAN Volume Controller V4.2.1 - Software Installation and Configuration Guide


SAN Router Technologies:

There are distance restrictions imposed due to latency. The amount of latency which can be tolerated depends on the type of copy services being used (Metro Mirror or Global Mirror). Details of the maximum latencies supported can be found in:

IBM System Storage SAN Volume Controller V4.2.1 - Software Installation and Configuration Guide



SAN Maintenance

A number of maintenance operations in SAN fabrics have been observed to occasionally cause IO errors for certain types of hosts. To avoid these errors, IO on these hosts must be quiesced prior to doing any type of SAN re-configuration activity, switch maintenance or SAN Volume Controller maintenance (see later section for Concurrent Code Load restrictions).

  1. Linux RH EL 2.1 AS and 3 AS
  2. Linux RH EL 4 AS (ppc64 only)



SAN Volume Controller Concurrent Code Load (CCL)

I/O errors have occasionally been observed during CCL with hosts running the operating system levels below. All IO should be quiesced on these systems before a software upgrade is started and should not be restarted until the code load is complete.
  1. Linux RH EL 2.1 AS and 3 AS
  2. Linux RH EL 4 AS (ppc64 only
  3. Solaris 9 on SBus based systems
  4. HP-UX 11iv2 on Itanium with pvlinks multipathing

Prior to starting a software upgrade, the SAN Volume Controller error log must be checked and any error conditions must be resolved and marked as fixed. All host paths must be online, and fabric must be fully redundant with no failed paths. If inter-cluster Remote Copy is being used, the same checks must be made on the remote cluster.


Maximum Configurations

Ensure that you are familiar with the maximum configurations of the SAN Volume Controller.

For SVC V4.2.0 maximum configurations please refer to the V4.2.0 Configurations and Guidelines.

For SVC V4.2.1 maximum configurations please refer to the table below:

Objects
Maximum Number
Comments
SVC Cluster
Nodes per cluster
8
Arranged as four I/O groups
Nodes per fabric
32
Maximum number of nodes that can be present on the same fabric, with visibility of each other
I/O Groups per cluster
4
Each containing two nodes
Fabrics per cluster
4
The number of counterpart SANs which are supported
Managed Disks
Managed disks (mdisks)
4096
The maximum number of logical units which can be managed by SVC. The number includes disks which have not been configured into managed disk groups
Managed disk groups
128
Mdisks per mdisk group
128
Mdisk size
2 TB
Total storage manageable per cluster
8 PB
If maximum extent size of 2048 MB used
Virtual Disks
Virtual disks (vdisks) per cluster
4096
Includes managed-mode vdisks and image-mode vdisks. Maximum requires an 8 node cluster
Vdisks per I/O group
1024
Vdisks per mdisk group
N/A
Cluster limit applies
Vdisk size
2 TB
Vdisks per host object
512
The limit may be different based on host operating system. See Host Attachment Guide for details
SDD
512 SAN Volume Controller vpaths per host
One vpath is created for each vdisk mapped to a host. Although the SAN Volume Controller permits 512 vdisks to be mapped to a host, the SDD limit can be exceeded by either :
  • Creating two (or more) host objects for one physical host and mapping more than 512 vdisks to the host using the multiple host objects
  • Creating two (or more) clusters and mapping more than 512 vdisks to the host using the multiple clusters

    Note : Both of these operations are unsupported for SDD
    • SDDPCM (on AIX)
    12,000 vpaths per host
    Vdisk-to-host mappings
    20,000
    Hosts / Servers
    Host ID's per cluster
    1024 - Cisco, Brocade and McDATA fabrics

    155 - CNT

    256 - Qlogic
    A Host ID is a collection of worldwide port names (WWPNs) which represents a host. This is used to associate SCSI LUNs with vdisks.

    See Also - Host ID's per I/O group below.

    For Brocade support, please see Note 2 below this table.
    Host ports per cluster
    2048 - Cisco, McDATA and Brocade fabrics

    310 - CNT

    512 - Qlogic
    Host IDs per I/O group
    256 - Cisco, McDATA and Brocade fabrics

    N/A - CNT

    64 - Qlogic
    Host ports per I/O group
    512 - Cisco, McDATA and Brocade fabrics

    N/A - CNT

    128 - Qlogic
    Hosts ports per host ID
    512
    Copy Services
    Metro Mirror or Global
    Mirror relationships per
    cluster
    1024
    Metro Mirror or Global
    Mirror consistency
    groups
    256
    Metro Mirror and
    Global Mirror vdisk per
    I/O group
    1024 TB
    There is a per I/O group limit of 1024TB on the quantity of Primary and Secondary vdisk address space which may participate in MetroMirror and Global Mirror relationships. This maximum
    configuration will consume all 512MB of bitmap space for the I/O Group and allow no FlashCopy bitmap space. The default is 40TB.
    FlashCopy targets
    per source
    16
    FlashCopy mappings
    3855
    Calculated by noticing that 240 source vdisks with 16 FC mappings plus one more with 15 mappings uses up all 4096 vdisks per cluster.
    FlashCopy mappings
    per consistency group
    512
    FlashCopy consistency
    groups
    128
    FlashCopy vdisk per
    I/O group
    1024 TB
    This is a per I/O group limit on the quantity of FlashCopy mappings using bitmap space from a given I/O Group. This maximum configuration will consume all 512MB of bitmap space for the I/O Group and allow no Metro or Global Mirror bitmap space. The default is 40TB.
    SVC Nodes
    Concurrent SCSI tasks
    (commands) per node
    10,000
    Concurrent commands
    per FC port
    2048
    Storage Controllers
    WWNNs
    64
    Some storage controllers have a separate WWNN per port e.g. Hitachi Thunder
    Storage controller
    WWPNs
    256
    LUNs per storage
    controller WWNN
    4096
    WWNNs per storage
    controller
    16
    The number of WWNNs per storage controller (Usually 1)
    WWPNs per WWNN
    16
    The maximum number of FC ports per worldwide node name

    Note 1: Fabric and Device Support
    A statement of support for a particular fabric configuration here is reflects the fact that SVC has been tested and is supported for attachment to that fabric configuration. Similarly a statement that SVC supports attachment to a particular backend device or host type reflects the fact that SVC has been tested and is supported for that attachment. SVC is only supported however for attachment to particular devices in a given fabric vendor if IBM and that fabric vendor both support that attachment. It is the user’s responsibility to verify that this is true for the particular configuration of interest as it is impossible to list individual ‘support’ or ‘no support’ statements for every possible intermix of front end and backend devices and fabric types.

    Note 2: Support for Brocade fabrics
    Support for Brocade fabrics with up to 1024 hosts is available on SVC V4.1.0.3 and later with the following restrictions.

    1. Fabrics that use M14, B64 or M48 switches in the core are supported. Any other supported Brocade switches may be used as edge switches in this configuration. The SVC ports and backend storage must all be connected to the core switches.

    2. The core M48 and B64s must be running at least the 5.1.0c firmware.

    3. The core M14s must be running at least the 5.0.5a firmware.

    Support of Brocade fabrics with up to 256 hosts is available on SVC V3.1.0.3 and later with the following restrictions.

    1. Only core-edge fabrics that use M14 or M48 switches in the core are supported. Any other supported Brocade switches may be used as edge switches in this configuration. The SVC ports and backend storage must all be connected to the core switches.

    2. Each SVC port must not see more than 512 N port logins. Error code 1800 is logged if this limit is exceeded on a Brocade fabric.

    3. Each I/O group may not be associated with more than 256 host objects.

    4. A host object may be associated with one or more I/O groups - if it is associated with more than one I/O group it counts towards the max 256 total in all of the I/O groups it is associated with.

    Note 3: Example bitmap usage
    FlashCopy: Each I/O group supports a default 40TB of target vdisks. The target vdisks may be in any I/O group. For the purpose of this limit vdisks are rounded up to a multiple of 8GB so 512 vdisks of 24.1GB will use all the bitmap space even though 512*24.1GB is less than 40TB.

    Example 1: You can make 1 copy of 40TB of vdisks in an I/O group to another 40TB of vdisks anywhere in the cluster

    Example 2: You can make 1 copy of 160TB of vdisks (40TB per I/O group) to another 160TB of vdisks anywhere in the cluster

    Example 3: You can make 10 copies of 4TB of vdisks in an I/O group onto another 40TB of vdisks anywhere in the cluster

    Metro Mirror and Global Mirror: Each I/O group supports a default 40TB of primary+secondary vdisk (that is 40TB shared between primary and secondary vdisks, not 40TB each). The 40TB can be split in any ratio between primary and secondary vdisk. For the purpose of this limit vdisks are rounded up to a multiple of 8GB. Metro Mirror and Global Mirror share the same bitmap memory - therefore the sum of primary Metro Mirror vdisks + primary Global Mirror vdisks + secondary Metro Mirror vdisks + secondary Global Mirror vdisks per I/O group is limited to 40TB.

    Example 1: You can use Metro Mirror or Global Mirror to copy 40TB of vdisks per I/O group to a secondary cluster for disaster recovery. You can also make a FlashCopy of your data at your primary and/or secondary cluster for backup

    Example 2: You can use intra-cluster Metro Mirror or Global Mirror to copy 20TB of vdisks per I/O group to another 20TB of vdisks in the same I/O group.
     
     
    		 

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    Document information
     Product categories:
     Hardware
     Computer Storage
     Storage Virtualization
     SAN Volume Controller
     IBM TotalStorage SAN Volume Controller Storage Engine
     V4.2.x
     Operating system(s):
      SAN Volume Controller
     Version:
      V4.2.x
     Reference #:
      S1003096
     IBM Group:
     Storage Systems Group
     Modified date:
     2009-09-01

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