Ve applicaons are less aected by table growth global

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Unformatted text preview: O request in parallel to as many disks as necessary to achieve the maximum bandwidth •  GPFS recognizes access paHerns such as: –  Sequen.al –  Reverse sequen.al CS480 Principles of Data Management Spring 2013 Data Striping and allocation (6/6) •  Striping works best when disks have equal size and performance •  Non ­uniform disk configura.on –  Trade ­off between throughput and space u.liza.on –  Maximizing space u.liza.on •  Placing more data on larger disks •  Smaller disks are under ­u.lized •  Propor.onally larger frac.on of I/O requests will be concentrated on the larger disks •  GPFS allows us to specify the policy to: –  Balance data placement for throughput or space u.liza.on 3 2/1/13 CS480 Principles of Data Management Spring 2013 CS480 Principles of Data Management •  Efficient file name lookup in very large directories (millions of files) –  Extensible hashing –  Organize directory entries Spring 2013 Large Directory Support (3/6) Extensible hashing Large Directory Support (1/6) •  Requires informa.on about ①  The key size (number of bits used) that maps the directory •  The global depth ②  The key size (number of bits used) that previously mapped the bucket The local depth •  •  Extensible hashing treats hash as a bit string ③  Capacity of the bucket –  Uses a tree data structure for bucket lookup –  Rehashing is done in an incremental fashion •  Time ­sensi.ve applica.ons are less affected by table growth •  Global depth: number of bits to represent the directory •  Local depth: number of bits to represent the entries in the bucket   The number of directory entries = 2global depth   The ini.al number of entries in the bucket = 2local depth CS480 Principles of Data Management Spring 20...
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