Tool to simulate non-sequential disk I/O (simulate db file sequential read) in C POSIX


 
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Old 06-18-2011
Happy with it not being completely random, as long as it jumps around enough to not catch itself on the read advance routines when running on the SAN, and as simulation goes, the database would more than likely read specific files or parts of files more than others anyway.

Here comes my next exciting problem, a database will only read a certain amount of time, other bits are sorting, writing and whatever else the database gets up to. So I am thinking of adding how manny cycles there are between reads, because just doing random reads and nothing else is giving rather silly results. In its purest form I seem to be able to get 100% WaitI/O and read about 6-12 Kb/s, which is pretty impressive in its ow right.

And todays exiting question, anyone feel like guessing how many cycles in a million that a rather streamlined database spends reading disk dataSmilie
Anyone who guesses the right answer wins an icecream, collectable in Camden, London (U.K.)

/Ben
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scsi_setup_cdb(9F)					   Kernel Functions for Drivers 					scsi_setup_cdb(9F)

NAME
scsi_setup_cdb - setup SCSI command descriptor block (CDB) SYNOPSIS
int scsi_setup_cdb(union scsi_cdb *cdbp, uchar_t cmd, uint_t addr, uint_t cnt, uint_t othr_cdb_data); INTERFACE LEVEL
Solaris DDI specific (Solaris DDI). PARAMETERS
cdbp Pointer to command descriptor block. cmd The first byte of the SCSI group 0, 1, 2, 4, or 5 CDB. addr Pointer to the location of the data. cnt Data transfer length in units defined by the SCSI device type. For sequential devices cnt is the number of bytes. For block devices, cnt is the number of blocks. othr_cdb_data Additional CDB data. DESCRIPTION
scsi_setup_cdb() function initializes a group 0, 1, 2, 4, or 5 type of command descriptor block pointed to by cdbp using cmd, addr, cnt, othr_cdb_data. addr should be set to 0 for commands having no addressing information (for example, group 0 READ command for sequential access devices). othr_cdb_data should be additional CDB data for Group 4 commands; otherwise, it should be set to 0. scsi_setup_cdb() function does not set the LUN bits in CDB[1] as the makecom(9F) functions do. Also, the fixed bit for sequential access device commands is not set. RETURN VALUES
scsi_setup_cdb() returns: 1 Upon success. 0 Upon failure. CONTEXT
These functions can be called from a user or interrupt context. SEE ALSO
makecom(9F), scsi_pkt(9S) Writing Device Drivers American National Standard Small Computer System Interface-2 (SCSI-2) American National Standard SCSI-3 Primary Commands (SPC) SunOS 5.10 23 Jun 1997 scsi_setup_cdb(9F)