The SCSI Reservation Mechanism
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- Most SCSI disks support a 'SCSI reservation' command.
- If a machine sent such a command to the disk, it works as a "lock"
against I/O coming from other machines.
- If a machine sends an I/O (read/write) request to a SCSI Disk reserved
by another machine, it will get an error, with a code of
- If the reserving machine crashes, another machine may send a
"break reservation" (or a "reset target") command, to brutally break the
- Of-course, now the second machine needs to send a SCSI reservation, before
sending any I/O to the device.
- This might cause file-system consistency problems (e.g. if the two
machines play too much with 'break reservation').