0610959fbb
Some iSCSI targets went with the traditional "export N ports" approach and then allowed the initiator to multipath over them. Other targets went the opposite direction and export a single port, and then software on the target side performs load balancing and failover to other targets via an iSCSI specific feature or IP takover. The problem for the 2nd type of config is we quickly run out of our five retries and get I/O errors. In these setups we want to reduce resource use on the initiator side so we only wanted the one session and no dm-multipath. To handle traditional multipath operations like failover we do IP takover on the target side. So we would have an iSCSI target running on node1. Some monitoring software decides it's dead or the node is overloaded so it starts the iSCSI target on node2. The problem is for the failover case where we might have the equivalent of a dm-multipath temporary all paths down, or we just have to try more than 5 nodes before finding a good one. To handle this type of issue allow the user to configure the disk cmd retries from -1 to the current max of 5. -1 means infinite retries and should be used for setups where some other setting is going to control when to fail. For example iSCSI has the replacement/recovery timeout and fc (some users have used FC with NPIV and done something similar as IP takover) has dev_loss_tmo/fast_io_fail which will eventually expire and fail I/O. Link: https://lore.kernel.org/r/1601566554-26752-3-git-send-email-michael.christie@oracle.com Reviewed-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Mike Christie <michael.christie@oracle.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.