Mitigating real node failure of a doubly mapped redundant array of independent nodes
Mitigating the effects of a real node failure in a doubly mapped redundant array of independent nodes, e.g., doubly mapped cluster is disclosed. In response to a change in an accessibility to data stored on an extent of a real storage device of a real node of a real cluster, wherein the extent of the real storage device corresponds to a portion of a mapped storage device of a mapped node of a doubly mapped cluster, substituting a reserved extent of a real storage device for the extent of the real storage device. The substituting the reserved extent of the real storage device can correspond to a change in a topology of the doubly mapped cluster, wherein the change in the topology comprises replacing the portion of the mapped storage device with a substitute portion of a mapped storage device that corresponds to the replacement extent of the real storage device. The changed topology can enable writing of data to the substituted portion of a mapped storage device that can cause writing of corresponding data to the reserved extent of the real storage device.
1. A system, comprising:
a processor; and
a memory that stores executable instructions that, when executed by the processor, facilitate performance of operations, comprising:
receiving an indication that a first extent of a first real storage device of a real cluster has become less accessible than a previous accessibility, wherein a doubly mapped cluster comprises the first extent, and wherein the real cluster comprises a second real storage device comprising a second extent;
based on the indication, substituting the second extent for the first extent that has become less accessible, wherein the substituting results in an updated mapping of the doubly mapped cluster corresponding to the real cluster being updated according to the substituting; and
performing a first data operation at the second extent based on receiving an instruction corresponding to the doubly mapped cluster and the updated mapping of the doubly mapped cluster corresponding to the real cluster.
2. The system of claim 1 , wherein the first extent of the first real storage device of the real cluster has become less accessible because a real node of the real cluster has become less accessible, wherein the real node comprises the real storage device, and wherein the real node does not comprise the second real storage device.
3. The system of claim 1 , wherein the first extent of the first real storage device of the real cluster has become less accessible as a result of a change in a network resource employed by the real cluster.
4. The system of claim 1 , wherein the first extent of the first real storage device of the real cluster has become less accessible as a result of a change in a storage resource employed by the real cluster.
5. The system of claim 1 , wherein the second extent is comprised in a group of reserved extents of the real cluster.
6. The system of claim 5 , wherein extents of the group of reserved extents of the real cluster are distributed among real storage devices of the real cluster.
7. The system of claim 6 , wherein the distribution of the extents among the real storage devices of the real cluster is an even distribution.
8. The system of claim 1 , wherein extents of the group of reserved extents of the real cluster are sufficient in number to enable substitution of each extent of storage devices of a first node of the real cluster, and wherein the storage devices of the first node comprise the first storage device.
9. The system of claim 1 , wherein the substituting the second extent for the first extent that has become less accessible is determined to satisfy a first rule related to node diversity.
10. The system of claim 1 , wherein a mapped storage device of a mapped node of the doubly mapped cluster comprises a first number of extents, and wherein the first real storage device comprises a second number of extents.
11. The system of claim 10 , wherein the first number of extents is greater than the second number of extents.
12. The system of claim 10 , wherein the first number of extents is less than the second number of extents.
13. The system of claim 10 , wherein the first number of extents is a same number of extents as the second number of extents.
14. A method, comprising:
in response to receiving an indication that a real cluster has become less accessible, updating, by a system comprising a processor, a mapping of extents of the real cluster mapped to a doubly mapped cluster resulting in an updated map, wherein the doubly mapped cluster comprises a first extent of a first disk of a first node of the real cluster, and wherein the updating the mapping is based on substituting a reserved extent of reserved extents of the real cluster for an extent of the extents of the real cluster to mitigate the real cluster becoming less accessible; and
writing, by the system, first data to the doubly mapped cluster based on the updated map, wherein the writing the first data facilitates mitigation of the real cluster becoming less accessible.
15. The method of claim 14 , wherein the receiving the indication that a real cluster has become less accessible is in response to determining, by the system, an occurrence of an event selected from a group of events comprising a hardware error in the real cluster, a software error in the real cluster, a change in a network resource employed by the real cluster, and a change in a storage resource employed by the cluster.
16. The method of claim 14 , wherein the substituting the reserved extent for the extent is determined, by the system, to satisfy a first rule related to node diversity.
17. The method of claim 14 , wherein the substituting the reserved extent comprises selecting, by the system, the reserved extent from the reserved extents, and wherein the reserved extents are uniformly distributed among storage devices of the real cluster.
18. A non-transitory machine-readable storage medium, comprising executable instructions that, when executed by a processor, facilitate performance of operations, comprising:
receiving an indication that a real cluster has become less accessible;
substituting a reserved extent of reserved extents of the real cluster for an extent of extents of the real cluster to mitigate the real cluster becoming less accessible, wherein the extent is comprised in a doubly mapped cluster comprising a first extent of a first disk of a first node of the real cluster;
determining an updated mapping between the extents of the real cluster and mapped extents of the doubly mapped cluster based on the substituting; and
causing a data operation to occur based on the updated mapping, wherein the data operation facilitates improved accessibility to the real cluster.
19. The non-transitory machine-readable medium of claim 18 , wherein a mapped disk of the doubly mapped cluster comprises a first count of the mapped extents that is different from a second count of the extents of a real disk of the real cluster.
20. The non-transitory machine-readable medium of claim 18 , wherein the updated mapping preserves node diversity of the doubly mapped cluster via preventing extents of any one real node of the real cluster from corresponding to mapped extents of any group of mapped nodes of the doubly mapped cluster.