InfoScale™ 9.0 Storage and Availability Management for DB2 Databases - AIX, Linux

read_pref_io

The preferred read request size. The file system uses this parameter in conjunction with the read_nstream value to determine how much data to read ahead. The default value is 64K.

write_pref_io

The preferred write request size. The file system uses this parameter in conjunction with the write_nstream value to determine how to do flush behind on writes. The default value is 64K.

read_nstream

The number of parallel read requests of size read_pref_io that you can have outstanding at one time. The file system uses the product of read_nstream multiplied by read_pref_io to determine its read ahead size. The default value for read_nstream is 1.

write_nstream

The number of parallel write requests of size write_pref_io that you can have outstanding at one time. The file system uses the product of write_nstream multiplied by write_pref_io to determine when to do flush behind on writes. The default value for write_nstream is 1.

discovered_direct_iosz

Any file I/O requests larger than the discovered_direct_iosz are handled as discovered direct I/O. A discovered direct I/O is unbuffered similar to direct I/O, but does not require a synchronous commit of the inode when the file is extended or blocks are allocated. For larger I/O requests, the CPU time for copying the data into the page cache and the cost of using memory to buffer the I/O data becomes more expensive than the cost of doing the disk I/O. For these I/O requests, using discovered direct I/O is more efficient than regular I/O. The default value of this parameter is 256K.

initial_extent_ size

Changes the default initial extent size. VxFS determines the size of the first extent to be allocated to the file based on the first write to a new file. Normally, the first extent is the smallest power of 2 that is larger than the size of the first write. If that power of 2 is less than 8K, the first extent allocated is 8K. After the initial extent, the file system increases the size of subsequent extents (see max_seqio_extent_size) with each allocation. Since most applications write to files using a buffer size of 8K or less, the increasing extents start doubling from a small initial extent. initial_extent_size can change the default initial extent size to be larger, so the doubling policy will start from a much larger initial size and the file system will not allocate a set of small extents at the start of file. Use this parameter only on file systems that will have a very large average file size. On these file systems, it will result in fewer extents per file and less fragmentation. initial_extent_size is measured in file system blocks.

max_direct_iosz

The maximum size of a direct I/O request that will be issued by the file system. If a larger I/O request comes in, then it is broken up into max_direct_iosz chunks. This parameter defines how much memory an I/O request can lock at once, so it should not be set to more than 20 percent of memory.

max_diskq

Limits the maximum disk queue generated by a single file. When the file system is flushing data for a file and the number of pages being flushed exceeds max_diskq, processes will block until the amount of data being flushed decreases. Although this doesn't limit the actual disk queue, it prevents flushing processes from making the system unresponsive. The default value is 1MB.

max_seqio_extent_size

Increases or decreases the maximum size of an extent. When the file system is following its default allocation policy for sequential writes to a file, it allocates an initial extent that is large enough for the first write to the file. When additional extents are allocated, they are progressively larger (the algorithm tries to double the size of the file with each new extent) so each extent can hold several writes' worth of data. This is done to reduce the total number of extents in anticipation of continued sequential writes. When the file stops being written, any unused space is freed for other files to use. Normally, this allocation stops increasing the size of extents at 2048 blocks, which prevents one file from holding too much unused space. max_seqio_extent_size is measured in file system blocks.

Enables or disables caching on Quick I/O files. The default behavior is to disable caching. To enable caching, set qio_cache_enable to 1. On systems with large memories, the database cannot always use all of the memory as a cache. By enabling file system caching as a second level cache, performance may be improved. If the database is performing sequential scans of tables, the scans may run faster by enabling file system caching so the file system will perform aggressive read-ahead on the files.

write_throttle