Fast destaging method using parity engine
First Claim
1. A fast destaging method using a parity engine, comprising the steps of:
- a. inspecting a read cache of a disk array after receiving a read request for a requested read block from a host system at the disk array;
b. returning the requested read block from the read cache if the requested read block is resident in the read cache and returning the requested read block from a disk after reading through the read cache if the requested read block is not resident in the read cache;
c. inspecting first a write cache and then a destaging cache of the disk array after receiving a write request for a requested write block from the host system at the disk array and writing the requested write block received from the host onto one of the write caches and the destaging cache if the requested write block is resident in the one of the write cache and the destaging cache;
d. determining whether there is an available block to allocate to the write cache if the requested write block is not resident in the one of the write cache and the destaging cache and routing the requested write block onto the available block if an available block is found;
e. moving a write cache block from the write cache to the destaging cache if no available block is found in said step d.;
f. reading an old data and an old parity of the write cache block and calculating a mid-parity therefrom;
g. determining whether the destaging cache is full after step f.;
h. writing the write request block to one of the write cache and the destaging cache if the destaging cache is determined not to be full in said step g.; and
i. generating a destaging by calculating a new parity from the mid-parity and a new data, writing a new parity block and a new data block onto each data disk and parity disk of said disk array, and writing the write request block to the write cache if the destaging cache is determined to be full in said step g.
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Abstract
The present invention relates to the fast destaging method using a parity engine, and more particularly to the fast destaging method for constituting and administering the cache of disk array in order to minimize lowering of write performance which occurs in high-speed disk array controller using VRAM parity engine.
According to the invention, the disk cache is composed of the read cache, the write cache and the destaging cache. The write caching is processed as being divided into the write cache and the destaging cache. The destaging cache, which has just one more block for mid parity to its data block, uses less memory and enables the write cache to be allocated with more blocks, and thereby it can improve hit ratio of cache. Write requests are first stored on the write cache, and if the write cache is full, they move blocks that would be least used thereafter into the destaging cache. Once destaging is requested, it is practicable with one parity calculation and two write operations by selecting blocks that is least recently used.
Also in destaging, block parity calculation can increase its speed and relieve the processor burden by using a VRAM based parity engine which has its dual ports.
31 Citations
3 Claims
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1. A fast destaging method using a parity engine, comprising the steps of:
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a. inspecting a read cache of a disk array after receiving a read request for a requested read block from a host system at the disk array; b. returning the requested read block from the read cache if the requested read block is resident in the read cache and returning the requested read block from a disk after reading through the read cache if the requested read block is not resident in the read cache; c. inspecting first a write cache and then a destaging cache of the disk array after receiving a write request for a requested write block from the host system at the disk array and writing the requested write block received from the host onto one of the write caches and the destaging cache if the requested write block is resident in the one of the write cache and the destaging cache; d. determining whether there is an available block to allocate to the write cache if the requested write block is not resident in the one of the write cache and the destaging cache and routing the requested write block onto the available block if an available block is found; e. moving a write cache block from the write cache to the destaging cache if no available block is found in said step d.; f. reading an old data and an old parity of the write cache block and calculating a mid-parity therefrom; g. determining whether the destaging cache is full after step f.; h. writing the write request block to one of the write cache and the destaging cache if the destaging cache is determined not to be full in said step g.; and i. generating a destaging by calculating a new parity from the mid-parity and a new data, writing a new parity block and a new data block onto each data disk and parity disk of said disk array, and writing the write request block to the write cache if the destaging cache is determined to be full in said step g. - View Dependent Claims (2, 3)
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Specification
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- Resources
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Current AssigneeElectronics and Telecommunications Research Institute
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Original AssigneeElectronics and Telecommunications Research Institute
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InventorsKim, Joong Bae, Kim, Jin Pyo, Yoon, Suk Han, Kim, Yong Yeon
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Primary Examiner(s)Chung, Phung M.
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Application NumberUS09/141,094Time in Patent Office601 DaysField of Search714/6, 714/805, 714/799, 714/800US Class Current714/805CPC Class CodesG06F 11/1076 Parity data used in redunda...G06F 12/0804 with main memory updating G...G06F 12/0866 for peripheral storage syst...G06F 2211/1009 Cache, i.e. caches used in ...G06F 2211/1059 Parity-single bit-RAID5, i....G06F 2212/312 In storage controller
