# US 9,519,438 B1 · Data migration between multiple tiers in a storage system using age and frequency statistics > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,519,438 B1 - Document ID: US9519438B1 - Status: Granted - Kind: B1 - Application number: 13/758,232 - Filed: 2013-02-04 - Granted: 2016-12-13 - Earliest claimed: 2007-04-13 - Assignees: American Megatrends, Inc. - Applicants: American Megatrends, Inc. - Inventors: Paresh Chatterjee; Ajit Narayanan; Loganathan Ranganathan; Sharon Enoch - Web page: https://patentgrep.com/patent/US9519438B1 ## CPC - G06F 3/0649: {Lifecycle management} - G06F 3/0604: {Improving or facilitating administration, e.g. storage management} - G06F 3/0685: {Hybrid storage combining heterogeneous device types, e.g. hierarchical storage, hybrid arrays} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract Technologies are described for implementing a migration mechanism in a storage system containing multiple tiers of storage with each tier having different cost and performance parameters. Access statistics can be collected for each territory, or storage entity, within the storage system. Data that is accessed more frequently can be migrated toward higher performance storage tiers while data that is accessed less frequently can be migrated towards lower performance storage tiers. The placement of data may be governed first by the promotion of territories with higher access frequency to higher tiers. Secondly, data migration may be governed by demoting territories to lower tiers to create room for the promotion of more eligible territories from the next lower tier. In instances where space is not available on the next lower tier, further demotion may take place to an even lower tier in order to make space for the first demotion. ## Claims ### Claim 1 A method for migrating data between tiers of a storage system, the method comprising: subdividing a storage capacity of the storage system into a set of territories; partitioning the set of territories into tiers; imposing an ordering on the tiers; maintaining an information lifecycle management metric for each territory, wherein maintaining an information lifecycle management metric comprises combining an age statistic and a frequency statistic into a single metric, wherein respective contributions of the age statistic and the frequency statistic to the single metric are mutually exclusive, and wherein the single metric is a signed value to indicate whether the single metric represents the age statistic or the frequency statistic, respectively; updating the information lifecycle management metric once per update period, wherein each update period has a consistent amount of time; promoting a territory that is more eligible into a highest possible tier in response to storage capacity being available in a higher tier; demoting a territory that is less eligible into a lower tier in response to a more eligible territory existing in the lower tier and no storage capacity being available for promotion of the more eligible territory; and demoting a least eligible territory to a next lowest tier in response to a less eligible territory existing in a next highest tier and no storage capacity being available for demotion of the less eligible territory. ### Claim 2 (depends on 1) The method of claim 1, wherein imposing an ordering on the tiers comprises ordering each one of the tiers higher in response to a respective tier having higher performance characteristics. ### Claim 3 (depends on 1) The method of claim 1, further comprising providing a periodic timer for scheduling of data migration. ### Claim 4 (depends on 1) The method of claim 1, further comprising providing a periodic timer for updating information lifecycle management metrics, wherein the periodic timer establishes the update period. ### Claim 5 (depends on 4) The method of claim 4, further comprising incrementing an age statistic associated with at least one territory in response to the periodic timer for updating information lifecycle management metrics. ### Claim 6 (depends on 5) The method of claim 5, wherein the age statistic associated with the at least one territory is incremented in response to the at least one territory not being accessed during the update period. ### Claim 7 (depends on 4) The method of claim 4, further comprising incrementing a frequency statistic associated with at least one territory during the update period. ### Claim 8 (depends on 7) The method of claim 7, wherein the frequency statistic associated with the at least one territory is incremented in response to the at least one territory being accessed during the update period. ### Claim 9 (depends on 1) The method of claim 1, further comprising sorting the territories within each tier in order of the information lifecycle management metric associated with each respective territory. ### Claim 10 A non-transitory computer storage medium having computer-executable instructions stored thereon which, when executed by a computer system, cause the computer system to: subdivide a storage capacity of a storage system into a set of territories; partition the set of territories into ordered tiers; maintain an information lifecycle management metric for each territory, wherein maintaining an information lifecycle management metric comprises combining an age statistic and a frequency statistic into a single metric, wherein respective contributions of the age statistic and the frequency statistic to the single metric are mutually exclusive, and wherein the single metric is a signed value to indicate whether the single metric represents the age statistic or the frequency statistic, respectively; update the information lifecycle management metric once per update period, wherein each update period has a consistent amount of time; promote a territory that is more eligible into a highest possible tier in response to storage capacity being available in a higher tier; demote a territory that is less eligible into a lower tier in response to a more eligible territory existing in the lower tier and no storage capacity being available for promotion of the more eligible territory; and demote a least eligible territory to a next lowest tier in response to a less eligible territory existing in a next highest tier and no storage capacity being available for demotion of the less eligible territory. ### Claim 11 (depends on 10) The non-transitory computer storage medium of claim 10, further causing the computer system to impose an ordering on the tiers by ordering each one of the tiers higher in response to a respective tier having higher performance characteristics. ### Claim 12 (depends on 10) The non-transitory computer storage medium of claim 10, further causing the computer system to provide a periodic timer for scheduling of data migration. ### Claim 13 (depends on 10) The non-transitory computer storage medium of claim 10, further causing the computer system to provide a periodic timer for updating information lifecycle management metrics, wherein the periodic timer establishes the update period. ### Claim 14 (depends on 13) The non-transitory computer storage medium of claim 13, further causing the computer system to increment an age statistic associated with at least one territory when a frequency statistic associated with the at least one territory equals zero in response to the periodic timer for updating information lifecycle management metrics. ### Claim 15 (depends on 14) The non-transitory computer storage medium of claim 14, wherein the age statistic associated with the at least one territory is incremented in response to the at least one territory not being accessed during the update period. ### Claim 16 (depends on 10) The non-transitory computer storage medium of claim 10, further causing the computer system to sort the territories within each tier in order of information lifecycle management metrics associated with each respective territory. ### Claim 17 A data storage system comprising: a storage subsystem; a plurality of physical storage devices associated with the storage subsystem; and one or more data migration modules operable to cause the storage subsystem to: subdivide a storage capacity of the storage system into a set of territories; partition the set of territories into tiers; maintain an information lifecycle management metric for each territory, wherein maintaining an information lifecycle management metric comprises combining an age statistic and a frequency statistic into a single metric, wherein respective contributions of the age statistic and the frequency statistic to the single metric are mutually exclusive, and wherein the single metric is a signed value to indicate whether the single metric represents the age statistic or the frequency statistic, respectively; update the information lifecycle management metric once per update period, wherein each update period has a consistent amount of time; promote a territory that is more eligible into a highest possible tier in response to storage capacity being available in a higher tier; demote a territory that is less eligible into a lower tier in response to a more eligible territory existing in the lower tier and no storage capacity being available for promotion of the more eligible territory; and demote a least eligible territory to a next lowest tier in response to a less eligible territory existing in a next highest tier and no storage capacity being available for demotion of the less eligible territory. ### Claim 18 (depends on 17) The data storage system of claim 17, wherein the data migration modules are further operable to provide a periodic timer for scheduling of data migration. ### Claim 19 (depends on 17) The data storage system of claim 17, wherein the data migration modules are further operable to provide a periodic timer for updating information lifecycle management metrics, wherein the periodic timer establishes the update period. ### Claim 20 (depends on 19) The data storage system of claim 19, wherein the data migration modules are further operable to increment an age statistic associated with at least one territory in response to the periodic timer for updating information lifecycle management metrics.