Highly available external storage system

An information system comprising:

• a primary storage system having a primary disk controller a plurality of primary disks for storing data;
• and
• an external storage system connected for communication with said primary storage system, said external storage system including an external disk controller and a plurality of external disks for storing data, said external disks being configured in a RAID configuration to provide redundant protection against data loss in the event of failure of one or more of the external disks;
• wherein said primary storage system maps a first virtual device on the primary storage system to a first logical device in said external storage system, said first logical device being created from said plurality of external disks,
• wherein write data targeting said first virtual device as if it were a logical device in said primary storage system, is transferred by the primary storage system to the external storage system, said external storage system storing the write data in said first logical device,
• wherein the primary storage system periodically checks I/O performance of the external storage system by periodically accessing the first logical device that is used by said primary storage system to map the first virtual device,
• wherein the primary storage system assumes that one of said plurality of external disks that forms a part of the first logical device in said external storage system has failed when the I/O performance has decreased by a predetermined amount,
• wherein, when said primary storage system assumes that one of the plurality of second disks that forms a part of the first logical device has failed, said primary storage system automatically migrates data from the first logical device of said external storage system to a second logical device located on said primary storage system,
• wherein, during said migration, said primary storage system is able to continue to receive input/output (I/O) operations targeting said first virtual device by referring to a bitmap table maintained in the primary storage system to determine if a targeted logical block address has yet been migrated to the second logical device,
• wherein said primary storage system is configured to periodically access the first logical device in the external storage system to determine whether a throughput in response to an access request has decreased, and
• wherein said throughput of the external storage system is measured by read performance in response to the access request that decreases by said predetermined amount based on a need of the external storage system to reconstruct read data using parity information to retrieve the read data.

An information system comprising:

• a primary storage system, said primary storage system including a primary controller;
• a plurality of external storage systems, each said external storage system having an external disk controller and a plurality of external disks for storing data, said external disks being configured in a RAID configuration to provide redundant protection against data loss in the event of failure of one or more of the external disks, wherein said primary storage system uses virtual devices to treat logical devices in said external storage systems as if they are logical devices in said primary storage system;
• a first logical device formed in a first said external storage system from the plurality of said external disks, said first logical device being used by said primary storage system to create a first virtual device in the primary storage system;
• and
• a network connecting said primary storage system and said plurality of external storage systems for communication,
• wherein the primary storage system periodically checks I/O performance of the first external storage system by periodically accessing the first logical device that is used by said primary storage system for the first virtual device,
• wherein the primary storage system assumes that one of said plurality of external disks that forms a part of the first logical device in said first external storage system has failed when the I/O performance has decreased by a predetermined amount,
• wherein, when said primary storage system assumes that one of the plurality of second disks that forms a part of the first logical device has failed, said primary storage system migrates data from the first logical device of said first external storage system to a second logical device in a second said external storage system, said second logical device being used by said primary storage system to form a second virtual device,
• wherein said primary storage system is configured to periodically access the first logical device in the external storage system to determine whether a throughput in response to an access request has decreased, and
• wherein said throughput of the external storage system is measured by read performance in response to the access request that decreases by said predetermined amount based on a need of the external storage system to reconstruct read data using parity information to retrieve the read data.