[dm-devel] Block multipathing in an IP-SAN
Mike Christie
michaelc at cs.wisc.edu
Wed Nov 2 06:56:06 UTC 2005
goggin, edward wrote:
> I'm wondering about how block device multipathing works in conjunction with
> the high availability
> features of an IP-SAN.
>
> Does the iSCSI initiator's session layer's retransmission capability and the
> IP-takeover capability
> of IP-SAN switches eliminate the need for block device multipathing in an
> IP-SAN?
>
> Does the iSCSI initiator present redundant paths to the SCSI mid-layer?
>
> Do these answers differ with software verses hardware iSCSI initiators?
>
For linux mainline and what some distros carry, software will be similar
to HW iscsi becuase the linux-scsi community has not wanted MCS. For
software iscsi in mainline (open-iscsi/linux-iscsi-5) and RHEL 4
(linux-iscsi-4), you can use bonding or trunking - whatever you know it
as, and hide everything from the iSCSI and SCSI levels, or you can use
dm-multipath. To do the latter for software iscsi, the iscsi driver
creates a session to each portal, scans it, and dm-multipath/multipath
assembles dm devices like it would for FC. The softare drivers drivers
also support login redirect and some vendors use this for failover and
load balancing. I think qlogic also support this.
More information about the dm-devel
mailing list