When a volume is mapped, IBM Spectrum Virtualize software automatically assigns the next  available SCSI ID if none is specified. In addition, a unique identifier, called the  UID , is on  each volume. You can allocate the operating system volume of the SAN boot as the lowest SCSI ID (zero  for most hosts), and then allocate the various data disks. If you share a volume among  multiple hosts, consider controlling the SCSI ID so that the IDs are identical across the  hosts. This consistency ensures ease of management at the host level and prevents potential  issues during IBM Spectrum Virtualize updates and even node reboots, mostly for ESX  operating systems. If you are using image mode to migrate a host to IBM Spectrum Virtualize, allocate the  volumes in the same order that they were originally assigned on the host from the back-end  storage. The  lshostvdiskmap  command displays a list of VDisk (volumes) that are mapped to a host.  These volumes are recognized by the specified host. Example 7-1 shows the syntax of the  lshostvdiskmap  command that is used to determine the SCSI ID and the UID of volumes. Example 7-2 shows the results of using the  lshostvdiskmap  command. Note:  Example 7-2 shows the same volume mapped to five different hosts, but host 110  has a different SCSI ID from the other four hosts. This is an example of a  non-recommended practice which can lead to loss of access in some situations due to  SCSI ID mismatch. In this example,  VDisk 10  has a unique device identifier (UID, which is represented by the  UID field) of  6005076801958001500000000000000A  (see Example 7-3), but the SCSI_ id that  host2 uses for access is  0 . Example 7-3 VDisk 10 with a UID Example 7-2 Output of using the lshostvdiskmap command Example 7-1 The lshostvdiskmap command svcinfo lshostvdiskmap -delim svcinfo lsvdiskhostmap -delim : EEXCLS_HBin01 id:name: SCSI_id :host_id:host_name:wwpn:vdisk_UID  950:EEXCLS_HBin01:14:109:HDMCENTEX1N1:10000000C938CFDF:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:109:HDMCENTEX1N1:10000000C938D01F:600507680191011D4800000000000466  950:EEXCLS_HBin01: 13 :110:HDMCENTEX1N2:10000000C938D65B:600507680191011D4800000000000466  950:EEXCLS_HBin01: 13 :110:HDMCENTEX1N2:10000000C938D3D3:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:111:HDMCENTEX1N3:10000000C938D615:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:111:HDMCENTEX1N3:10000000C938D612:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:112:HDMCENTEX1N4:10000000C938CFBD:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:112:HDMCENTEX1N4:10000000C938CE29:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:113:HDMCENTEX1N5:10000000C92EE1D8:600507680191011D4800000000000466  950:EEXCLS_HBin01:14:113:HDMCENTEX1N5:10000000C92EDFFE:600507680191011D4800000000000466 id:name:SCSI_id:vdisk_id:vdisk_name:wwpn:vdisk_UID  2:host2:0:10: vdisk10 :0000000000000ACA: 6005076801958001500000000000000A 2:host2:1:11:vdisk11:0000000000000ACA:6005076801958001500000000000000B  2:host2:2:12:vdisk12:0000000000000ACA:6005076801958001500000000000000C  Chapter 7. Hosts  247