# US 2014/0157049 A1 · System and method for enhancing availability of a distributed object storage system during a partial database outage > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0157049 A1 - Document ID: US20140157049A1 - Status: Published application - Kind: A1 - Application number: 13/924,666 - Filed: 2013-06-24 - Published: 2014-06-05 - Earliest claimed: 2010-09-24 - Assignees: Hitachi Data Systems Corporation - Applicants: Hitachi Data Systems Corporation - Inventors: Alan G. Bryant; Kevin S. Grimaldi; Trek Palmer; David B. Pinkney - Web page: https://patentgrep.com/patent/US20140157049A1 ## CPC - G06F 11/1464: {for networked environments} - G06F 3/0619: {in relation to data integrity, e.g. data losses, bit errors} - G06F 3/065: {Replication mechanisms} - G06F 3/067: {Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]} - G06F 11/1425: {by reconfiguration of node membership} - G06F 11/143: {with loss of software functionality} - G06F 11/1435: {using file system or storage system metadata} - G06F 11/1451: {by selection of backup contents} - G06F 11/1662: {the resynchronized component or unit being a persistent storage device (re-synchronization of failed mirror storage G06F11/2082; rebuild or reconstruction of parity RAID storage G06F11/1008)} - G06F 11/2094: {Redundant storage or storage space (G06F11/2056 takes precedence)} - G06F 2201/80: Database-specific techniques - G06F 2201/84: Using snapshots, i.e. a logical point-in-time copy of the data - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract An “operate with missing region” feature allows a cluster to continue servicing reads for available regions even when some regions are missing. Upon a given node failure condition, the cluster is placed in an effective read-only mode for all regions. The node failure condition typically is one where there has been a failure of an authoritative region copy and no backup copy is then available. Typically, “read-only” means no client write or update requests succeed while the cluster is in this state. Those requests should fail with an error message that indicates failure because of the read-only status. Preferably, such requests are re-tried. In this mode, regions are only allowed to perform read operations but the cluster continues to operate with missing regions, and missing regions are entered on a region map. The cluster then automatically recovers returning missing regions, after which it leaves the read-only state. ## Claims ### Claim 1 A method for a computer system having a plurality of nodes, wherein metadata objects are stored in a set of regions distributed across the plurality of nodes, the method comprising: distributing an authoritative region copy in the plurality of nodes, the authoritative region copy being configured to receive requests to the region in the set of regions; distributing a backup region copy in the plurality of nodes, the backup region copy being configured to synchronize with the authoritative region copy; if the authoritative region copy fails and the backup region copy is available, promoting, using software executing in a hardware element, the backup region copy to the authoritative region copy; and if the authoritative region copy fails and no backup region copy is available, entering a read-only state for all regions in the set of regions distributed across the plurality of nodes. ### Claim 2 (depends on 1) The method as described in claim 1, further including: distributing, across the plurality of nodes, region maps identifying the set of regions among the plurality of nodes; and indicating, in the region maps, a missing region, the missing region corresponding to a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 3 (depends on 1) The method as described in claim 1, further comprising: during the read-only state, creating a proxy copy for a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 4 (depends on 1) The method as described in claim 1, further comprising: during the read-only state, returning an error for a read request to the authoritative region copy that has failed, while processing a read request directed to other than the authoritative region copy that has failed. ### Claim 5 (depends on 1) The method as described in claim 1, further comprising: during the read-only state, having at least one node other than the node that supports the authoritative region copy that has failed respond to a client request. ### Claim 6 (depends on 1) The method as described in claim 1, further comprising: recovering a missing region and leaving the read-only state following such recovery. ### Claim 7 A computer system, comprising: a plurality of nodes, wherein metadata objects are stored in a set of regions distributed across the plurality of nodes; an authoritative region copy distributed in the plurality of nodes, the authoritative region copy being configured to receive requests to the region in the set of regions; and a backup region copy distributed in the plurality of nodes, the backup region copy being configured to synchronize with the authoritative region copy; the backup region copy adapted to being promoted to the authoritative region copy if the authoritative region copy fails and the backup region copy is available; and wherein all regions in the set of regions distributed across the plurality of nodes operate in a read-only state if the authoritative region copy fails and no backup region copy is available. ### Claim 8 (depends on 7) The computer system as described in claim 7 further comprising: a set of region maps distributed across the plurality of nodes, the region maps identifying the set of regions among the plurality of nodes, and wherein a missing region in the region maps corresponds to a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 9 (depends on 7) The computer system as described in claim 7 further comprising: a proxy copy created during the read-only state, the proxy copy for a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 10 (depends on 7) The computer system as described in claim 7 wherein, during the read-only state, an error is returned for a read request to the authoritative region copy that has failed while a read request directed to other than the authoritative region copy that has failed is processed. ### Claim 11 (depends on 7) The computer system as described in claim 7, wherein, during the read-only state, at least one node other than the node that supports the failed authoritative region copy responds to a client request. ### Claim 12 (depends on 7) The computer system as described in claim 7, wherein a missing region is recovered and the read-only state is left following such recovery. ### Claim 13 A non-transitory computer-readable medium having stored thereon instructions that, when executed by a processor, perform a method operative in a plurality of nodes in which metadata objects are stored in a set of regions distributed across the plurality of nodes, the method comprising: distributing an authoritative region copy in the plurality of nodes, the authoritative region copy being configured to receive requests to the region in the set of regions; distributing a backup region copy in the plurality of nodes, the backup region copy being configured to synchronize with the authoritative region copy; if the authoritative region copy fails and the backup region copy is available, promoting, using software executing in a hardware element, the backup region copy to the authoritative region copy; and if the authoritative region copy fails and no backup region copy is available, entering a read-only state for all regions in the set of regions distributed across the plurality of nodes. ### Claim 14 (depends on 13) The non-transitory computer-readable medium as described in claim 13, wherein the method further includes: distributing, across the plurality of nodes, region maps identifying the set of regions among the plurality of nodes; and indicating, in the region maps, a missing region, the missing region corresponding to a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 15 (depends on 13) The non-transitory computer-readable medium as described in claim 13, wherein the method further comprises: during the read-only state, creating a proxy copy for a state wherein the authoritative region copy fails and no backup region copy is available. ### Claim 16 The non-transitory computer-readable medium as described in claim, wherein the method further comprises: during the read-only state, returning an error for a read request to the authoritative region copy that has failed, while processing a read request directed to other than the authoritative region copy that has failed. ### Claim 17 (depends on 13) The non-transitory computer-readable medium as described in claim 13, wherein the method further comprises: during the read-only state, having at least one node other than the node that supports the authoritative region copy that has failed respond to a client request. ### Claim 18 (depends on 13) The non-transitory computer-readable medium as described in claim 13, wherein the method further comprises: recovering a missing region and leaving the read-only state following such recovery.