Managing operation of a data storage system with reservation of metadata space

Patent metadata

Field	Value
Publication number	US-2021286518-A1
Application number	US-202016819595-A
Country	US
Kind code	A1
Filing date	Mar 16, 2020
Priority date	Mar 16, 2020
Publication date	Sep 16, 2021
Grant date	—

Abstract

A method of managing operation of a data storage system (DSS) is provided. The method includes (a) reserving space within a dedicated metadata storage region (DMSR); (b) in response to determining that accommodating a storage request requires use of the reserved space, entering a restricted write mode; (c) while operating in the restricted write mode, using the reserved space in a process that frees space within the DMSR outside the reserved space; and (d) exiting the restricted mode in response to freeing space within the DMSR outside the reserved space. An apparatus, system, and computer program product for performing a similar method are also provided.

First claim

1 . A method of managing operation of a data storage system (DSS), the method comprising:
reserving space within a dedicated metadata storage region (DMSR); in response to determining that accommodating a storage request requires use of the reserved space, entering a restricted write mode; while operating in the restricted write mode, using the reserved space in a process that frees space within the DMSR outside the reserved space; and exiting the restricted write mode in response to freeing space within the DMSR outside the reserved space.

2 . The method of claim 1 wherein operating the DSS in the restricted write mode includes refraining from accepting new write request from users.

3 . The method of claim 2 ,
wherein operating the DSS in the restricted write mode further includes accepting a user request to delete a particular logical disk; and wherein using the reserved space in the process that frees space within the DMSR outside the reserved space includes:
deleting, from the DMSR, metadata that organizes the particular logical disk and
adding pointers to the deleted metadata to a free list, the free list being at least partially stored within the reserved space.

4 . The method of claim 2 ,
wherein operating the DSS in the restricted write mode further includes accepting a user request to delete a particular snapshot of a logical disk; and wherein using the reserved space in the process that frees space within the DMSR outside the reserved space includes:
deleting, from the DMSR, metadata that organizes the particular snapshot of the logical disk and
adding pointers to the deleted metadata to a free list, the free list being at least partially stored within the reserved space.

5 . The method of claim 2 wherein operating the DSS in the restricted write mode further includes accepting read request from users.

6 . The method of claim 2 wherein the method further comprises, while operating in the restricted write mode, flushing cached metadata from a metadata cache into the reserved space, the cached metadata representing write operations received by the DSS prior to entering the restricted write mode.

7 . The method of claim 6 wherein reserving space within the DMSR includes reserving at least as much space as a capacity of the metadata cache.

8 . The method of claim 1 wherein determining that accommodating the storage request requires use of the reserved space includes:
attempting to allocate additional space for the DMSR; and
failing to allocate the additional space.

9 . The method of claim 8 wherein exiting the restricted write mode in response to freeing space within the DMSR outside the reserved space includes successfully allocating additional space for the DMSR.

10 . The method of claim 1 wherein determining that accommodating the storage request requires use of the reserved space includes:
calculating a remaining amount, R, of space in the DMSR;
determining an amount, N, of new metadata needed to accommodate the storage request; and
given a size, P, of the reserved space, determining that R−N<P.

11 . The method of claim 10 wherein calculating the remaining amount, R, of space in the DMSR includes:
reading a cursor value of the DMSR, the cursor value indicating a lowest address of the DMSR to which metadata has not yet been written;
subtracting the cursor value from an allocated size of the DMSR to yield an intermediate result;
determining an amount of empty space within the DMSR below the cursor value by reading pointers from a list of freed blocks of metadata; and
summing the intermediate result and the determined amount of empty space within the DMSR below the cursor value.

12 . The method of claim 1 ,
wherein entering the restricted write mode includes storing an indication of being in the restricted write mode within a specific portion of persistent storage; and wherein the method further comprises, in response to the DSS rebooting after a failure, reading the indication of being in the restricted write mode from the specific portion of persistent storage, and, in response, re-entering the restricted write mode.

13 . A computer program product comprising a non-transitory computer-readable storage medium storing a set of instructions, which, when performed by processing circuitry of a data storage apparatus (DSA), causes the processing circuitry to manage operation of the DSA by:
reserving space within a dedicated metadata storage region (DMSR); in response to determining that accommodating a storage request requires use of the reserved space, entering a restricted write mode; while operating in the restricted write mode, using the reserved space in a process that frees space within the DMSR outside the reserved space; and exiting the restricted write mode in response to freeing space within the DMSR outside the reserved space.

14 . A data storage apparatus (DSA) comprising:
a plurality of non-transitory persistent storage drives; and processing circuitry coupled to memory configured to manage operation of the DSA by:
reserving space within a dedicated metadata storage region (DMSR);
in response to determining that accommodating a storage request requires use of the reserved space, entering a restricted write mode;
while operating in the restricted write mode, using the reserved space in a process that frees space within the DMSR outside the reserved space; and
exiting the restricted write mode in response to freeing space within the DMSR outside the reserved space.

Assignees

• Emc Ip Holding Co Llc

Inventors

• Li Xiongcheng
• Vankamamidi Vamsi K
• Xu Xinlei
• Gao Jian
• Han Geng

Classifications

• G06F3/061

  Improving I/O performance · CPC title

• G06F3/0671

  In-line storage system · CPC title

• G06F3/0634 Primary

  by changing the state or mode of one or more devices · CPC title

• G06F3/0644

  Management of space entities, e.g. partitions, extents, pools · CPC title

• G06F3/0679

  Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP] · CPC title