Date: Tue, 23 Feb 2010 18:44:41 +0100 From: Harald Schmalzbauer <h.schmalzbauer@omnilan.de> To: Alexander Motin <mav@FreeBSD.org> Cc: freebsd-stable@FreeBSD.org Subject: Re: ahcich timeouts, only with ahci, not with ataahci Message-ID: <4B841409.5070603@omnilan.de> In-Reply-To: <4B8411EE.5030909@FreeBSD.org> References: <1266934981.00222684.1266922202@10.7.7.3> <4B83EFD4.8050403@FreeBSD.org> <4B83FD62.2020407@omnilan.de> <4B83FFEF.7010509@FreeBSD.org> <4B840C54.3010304@omnilan.de> <4B8411EE.5030909@FreeBSD.org>
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[-- Attachment #1 --] Alexander Motin schrieb am 23.02.2010 18:35 (localtime): ... >> One understanding question: If the drive doesn't complete a command, >> regardless if it's due to a firmware bug, a disk surface error or >> whatever, is there no way for the driver to terminate the request and >> take the drive offline after some time? This would be a very important >> behaviour for me. It doesn't make sense building RAIDz storage when a >> failing drive hangs the complete machine, even if the system partitions >> are on a complete different SSD. > > That's what timeouts are used for. When timeout detected, driver resets > device and reports error to upper layer. After receiving error, CAM > reinitializes device. If device is completely dead, reinitialization > will fail and device will be dropped immediately. If device is still > alive, reinit succeed and CAM will retry command again. If all retries > failed, error reported to the GEOM layer and then possibly to file > system. I have no idea how RAIDZ behaves in such case. May be after few > such errors it should drop that device out of array. > > Timeout is a worst possible case for any device, as it takes too much > time and doesn't give any recovery information. Half-dead case is worst > possible case of timeout. It is difficult to say what which way is > better: drop last drive from degraded array and lost all info, or retry > forever. There is probably no right answer. I see. Thanks a lot for clarification. Before getting the machine onsite I did some ZFS tests like removing one disk when cvs checkout was running. I can remember that ZFS hadn't showed the removed drive as offline, but there was no hang. The pool was degraded and after reinserting and rebooting I could resilver the pool. I couldn't manage to get it consistent without rebooting, but I accepted that since I would have to walk on site for changing the drive any way. I'll restore the default vfs.zfs.txg.timeout=30, so the hang can be easily reproduced and see if I can 'camcontrol stop' the drive. Do you think I can get usefull information with that test? Thanks, -Harry [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.13 (FreeBSD) iEYEARECAAYFAkuEFAkACgkQLDqVQ9VXb8h4MwCfUKBtFqeqn+MqktUGTsTRqV2T H7gAn3Ki2R5zTt0Zv65fn0yrpmaDqQ9F =2cn/ -----END PGP SIGNATURE-----
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