Accessing data in a dispersed storage network during write operations

• US 10,025,505 B2
• Filed: 06/29/2016
• Issued: 07/17/2018
• Est. Priority Date: 06/29/2016
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Baptist, Andrew D., Dhuse, Greg R., Khadiwala, Ravi V., Volvovski, Ilya
• Primary Examiner(s): Chappell, Daniel C
• Application Number:
  US15/196,312
• Publication Number:
  US 20180004427A1
• Time in Patent Office: 748 Days
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

A method includes sending data access requests to storage units regarding a set of encoded data slices. The method further includes, when a write transaction is pending for the set of encoded data slices, receiving proposal records from the storage units. The method further includes interpreting the proposal records to determine an ordering of visible versions of the set of encoded data slices stored by the storage units. The method further includes determining whether a threshold number of encoded data slices of a desired version of the set of encoded data slices is visible. The method further includes, when the threshold number of encoded data slices is visible, determining whether to proceed with the data access request. The method further includes, when determined to proceed with the data access request, sending a request to proceed with the data access request to the storage units.

Claims

1. A method comprises:

sending, by a computing device, data access requests to storage units of a dispersed storage network (DSN) regarding a set of encoded data slices, wherein one of the data access requests includes a slice name for a corresponding one of the encoded data slices of the set of encoded data slices, a transaction number, a type of request, and a current revision level of the encoded data slice;

when a transaction is pending for the set of encoded data slices, receiving, by the computing device, proposal records from the storage units, wherein the proposal records include an ordered list of pending transactions for an encoded data slice of the set of encoded data slices, an indication of the current revision level, and an ordered list of different versions of the encoded data slice;

interpreting, by the computing device, the proposal records to determine an ordering of visible versions of the set of encoded data slices stored by the storage units, wherein the interpreting includes reading the ordered list of different versions of the encoded data slice to identify a first priority version of the encoded data slice and a second priority version of the encoded data slice, wherein priority of the first priority version is higher than priority of the second priority version;

determining, by the computing device, whether a threshold number of encoded data slices of a desired version of the set of encoded data slices is visible and of priority;

when the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible and of priority, determining, by the computing device, whether to proceed with the data access request; and

when the computing device determines to proceed with the data access request, sending, by the computing device, a request to proceed with the data access request to the storage units.

2. The method of claim 1 further comprises:

the ordered list of pending transactions including, in order, a first write request regarding the encoded data slice from a first writing computing device and a second write request regarding the encoded data slice from a second writing computing device, wherein each of the first and second write requests includes a transaction number, the slice name of the encoded data slice, a version of the encoded data slice, and the current revision level of the encoded data slice; and

the ordered list of different version of the encoded data slice including, in order, the current revision level of the encoded data slice, a first version of the encoded data slice from the first writing computing device, and a second version of the encoded data slice from the second writing computing device.

3. The method of claim 1, wherein the determining whether the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible comprises:

selecting the desired version of the set of encoded data slices from a list that includes one or more of the current revision level of the set of encoded data slices, a first version of the set of encoded data slices from a first writing computing device, and a second version of the set of encoded data slices from a second writing computing device;

when the current revision level of the set of encoded data slices is selected as the desired version of the set of encoded data slices, indicating that there is the threshold number of encoded data slices is visible; and

when the first version or the second version of the set of encoded data slices is selected as the desired version of the set of encoded data slices;

determining whether the selected version of the set of encoded data slices has a consensus of ordered positioning to execute a finalize command; and

when the selected version of the set of encoded data slices has the consensus of ordered positioning to execute a finalize command, indicating that there is the threshold number of encoded data slices is visible.

4. The method of claim 1 further comprises:

determining to proceed with the data access request when the data access request is a read request;

sending a read fulfillment request to at least some of the storage units; and

receiving, in response to the read fulfillment request, at least a decode threshold number of encoded data slices of the desired version of the set of encoded data slices from the at least some of the storage units.

5. The method of claim 1 further comprises:

determining to proceed with the data access request when the data access request is a write request regarding the desired version of the set of encoded data slices; and

sending a write finalize request to the storage units.

6. The method of claim 1 further comprises:

determining not to proceed with the data access request when the data access request is a write request and the write request is not regarding the desired version of the set of encoded data slices; and

sending an undo command to the storage units.

7. A computing device comprises:

an interface for interfacing with a network;

memory; and

a processing module operably coupled to the interface and to the memory, wherein the processing module is operable to;

send, via the interface, data access requests to storage units of a dispersed storage network (DSN) regarding a set of encoded data slices, wherein one of the data access request includes a slice name for a corresponding one of the encoded data slices of the set of encoded data slices, a transaction number, a type of request, and a current revision level of the encoded data slice;

when a transaction is pending for the set of encoded data slices, receive, via the interface, proposal records from the storage units, wherein the proposal records include an ordered list of pending transactions for an encoded data slice of the set of encoded data slices, an indication of the current revision level, and an ordered list of different versions of the encoded data slice;

interpret the proposal records to determine an ordering of visible versions of the set of encoded data slices stored by the storage units, wherein the interpreting includes reading the ordered list of different versions of the encoded data slice to identify a first priority version of the encoded data slice and a second priority version of the encoded data slice, wherein priority of the first priority version is higher than priority of the second priority version;

determine whether a threshold number of encoded data slices of a desired version of the set of encoded data slices is visible;

when the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible, determine whether to proceed with the data access request; and

when the computing device determines to proceed with the data access request, send, via the interface, a request to proceed with the data access request to the storage units.

8. The computing device of claim 7 further comprises:

the ordered list of pending transactions including, in order, a first write request regarding the encoded data slice from a first writing computing device and a second write request regarding the encoded data slice from a second writing computing device, wherein each of the first and second write requests includes a transaction number, the slice name of the encoded data slice, a version of the encoded data slice, and the current revision level of the encoded data slice; and

the ordered list of different version of the encoded data slice including, in order, the current revision level of the encoded data slice, a first version of the encoded data slice from the first writing computing device, and a second version of the encoded data slice from the second writing computing device.

9. The computing device of claim 7, wherein the processing module is further operable to determine whether the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible by:

selecting the desired version of the set of encoded data slices from a list that includes one or more of the current revision level of the set of encoded data slices, a first version of the set of encoded data slices from a first writing computing device, and a second version of the set of encoded data slices from a second writing computing device;

when the current revision level of the set of encoded data slices is selected as the desired version of the set of encoded data slices, indicating that there is the threshold number of encoded data slices is visible; and

when the first version or the second version of the set of encoded data slices is selected as the desired version of the set of encoded data slices;

determining whether the selected version of the set of encoded data slices has a consensus of ordered positioning to execute a finalize command; and

when the selected version of the set of encoded data slices has the consensus of ordered positioning to execute a finalize command, indicating that there is the threshold number of encoded data slices is visible.

10. The computing device of claim 7, wherein the processing module is further operable to:

when the data access request is a read request;

send, via the interface, a read fulfillment request to at least some of the storage units; and

receive, via the interface and in response to the read fulfillment request, at least a decode threshold number of encoded data slices of the desired version of the set of encoded data slices from the at least some of the storage units;

when the data access request is a write request regarding the desired version of the set of encoded data slices;

determine to proceed with the data access request;

send, via the interface, a write finalize request to the storage units;

when the data access request is a write request and the write request is not regarding the desired version of the set of encoded data slices;

determine not to proceed with the data access request; and

send, via the interface, an undo command to the storage units.

11. A computer readable memory comprises:

a first memory element that stores operational instructions that, when executed by a computing device, causes the computing device to;

send data access requests to storage units of a dispersed storage network (DSN) regarding a set of encoded data slices, wherein one of the data access request includes a slice name for a corresponding one of the encoded data slices of the set of encoded data slices, a transaction number, a type of request, and a current revision level of the encoded data slice;

a second memory element that stores operational instructions that, when executed by the computing device, causes the computing device to;

when a transaction is pending for the set of encoded data slices, receive proposal records from the storage units, wherein a proposal record of the proposal records includes an ordered list of pending transactions for an encoded data slice of the set of encoded data slices, an indication of the current revision level, and an ordered list of different versions of the encoded data slice;

a third memory element that stores operational instructions that, when executed by the computing device, causes the computing device to;

interpret the proposal records to determine an ordering of visible versions of the set of encoded data slices stored by the storage units, wherein the interpreting includes reading the ordered list of different versions of the encoded data slice to identify a first priority version of the encoded data slice and a second priority version of the encoded data slice, wherein priority of the first priority version is higher than priority of the second priority version;

determine whether a threshold number of encoded data slices of a desired version of the set of encoded data slices is visible;

when the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible, determine whether to proceed with the data access request; and

when the computing device determines to proceed with the data access request, send a request to proceed with the data access request to the storage units.

12. The computer readable memory of claim 11 further comprises:

the ordered list of pending transactions including, in order, a first write request regarding the encoded data slice from a first writing computing device and a second write request regarding the encoded data slice from a second writing computing device, wherein each of the first and second write requests includes a transaction number, the slice name of the encoded data slice, a version of the encoded data slice, and the current revision level of the encoded data slice; and

the ordered list of different version of the encoded data slice including, in order, the current revision level of the encoded data slice, a first version of the encoded data slice from the first writing computing device, and a second version of the encoded data slice from the second writing computing device.

13. The computer readable memory of claim 11, wherein the third memory element further stores operational instructions that, when executed by the computing device, causes the computing device to determine whether the threshold number of encoded data slices of a desired version of the set of encoded data slices is visible by:

selecting the desired version of the set of encoded data slices from a list that includes one or more of the current revision level of the set of encoded data slices, a first version of the set of encoded data slices from a first writing computing device, and a second version of the set of encoded data slices from a second writing computing device;

when the current revision level of the set of encoded data slices is selected as the desired version of the set of encoded data slices, indicating that there is the threshold number of encoded data slices is visible; and

when the first version or the second version of the set of encoded data slices is selected as the desired version of the set of encoded data slices;

determining whether the selected version of the set of encoded data slices has a consensus of ordered positioning to execute a finalize command; and

when the selected version of the set of encoded data slices has the consensus of ordered positioning to execute a finalize command, indicating that there is the threshold number of encoded data slices is visible.

14. The computer readable memory of claim 11, wherein the third memory element further stores operational instructions that, when executed by the computing device, causes the computing device to:

when the data access request is a read request;

send a read fulfillment request to at least some of the storage units; and

receive, in response to the read fulfillment request, at least a decode threshold number of encoded data slices of the desired version of the set of encoded data slices from the at least some of the storage units;

when the data access request is a write request regarding the desired version of the set of encoded data slices;

determine to proceed with the data access request;

send a write finalize request to the storage units;

when the data access request is a write request and the write request is not regarding the desired version of the set of encoded data slices;

determine not to proceed with the data access request; and

send an undo command to the storage units.