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Brian Behlendorf
a69052be7f
While there is no right maximum timeout for a disk IO we can start laying the ground work to measure how long they do take in practice. This change simply measures the IO time and if it exceeds 30s an event is posted for 'zpool events'. This value was carefully selected because for sd devices it implies that at least one timeout (SD_TIMEOUT) has occured. Unfortunately, even with FAILFAST set we may retry and request and not get an error. This behavior is strongly dependant on the device driver and how it is hooked in to the scsi error handling stack. However by setting the limit at 30s we can log the event even if no error was returned. Slightly longer term we can start recording these delays perhaps as a simple power-of-two histrogram. This histogram can then be reported as part of the 'zpool status' command when given an command line option. None of this code changes the internal behavior of ZFS. Currently it is simply for reporting excessively long delays.
Native ZFS for Linux! ZFS is an advanced file system and volume manager which was originally developed for Solaris. It has been successfully ported to FreeBSD and now there is a functional Linux ZFS kernel port too. The port currently includes a fully functional and stable SPA, DMU, and ZVOL with a ZFS Posix Layer (ZPL) on the way!
$ ./configure
$ make pkg
Full documentation for building, configuring, and using ZFS can be found at: http://zfsonlinux.org