Date: Wed, 14 Oct 1998 11:52:59 -0700 From: Don Lewis <Don.Lewis@tsc.tdk.com> To: "Justin T. Gibbs" <gibbs@plutotech.com>, Don Lewis <Don.Lewis@tsc.tdk.com> Cc: Terry Lambert <tlambert@primenet.com>, freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG Subject: Re: filesystem safety and SCSI disk write caching Message-ID: <199810141852.LAA19279@salsa.gv.tsc.tdk.com> In-Reply-To: "Justin T. Gibbs" <gibbs@plutotech.com> "Re: filesystem safety and SCSI disk write caching" (Oct 14, 12:01am)
next in thread | previous in thread | raw e-mail | index | archive | help
On Oct 14, 12:01am, "Justin T. Gibbs" wrote: } Subject: Re: filesystem safety and SCSI disk write caching } >} The drive will reinitialize to the 'power on state' if the power fluctuates } >} into a zone that might invalidate it's run-time state. It doesn't take a } >} very long spike for the drive's power-glitch sensor to go off. In this } >} case, dropping cached contents on the floor is much safer than attempting } >} to continue from an unknown state. } > } >If that's the reason for the problem that I saw, then the UPS the } >system was plugged into wasn't sufficient to prevent the problem. } } Why is that? Do you have gremlins walking around hitting the reset } buttons on your machines? The UPS should isolate the machine from } any drop in power that would cause it to lose its brain other than } that caused by a hardware failure or an administrator hitting the } reset or power switch. >From my point of view, I can cut the run time of something like "make buildworld" by about 25 percent by turning on softupdates. If I disable write caching on the drive, it increases the time by about 1 percent, but I don't have to worry about filesystem corruption caused by: gremlins hitting the reset button power glitches that cause the drive to forget uncommitted transactions firmware bugs that cause the drive to forget uncommitted transactions when the drive sees a SCSI reset the power supply fuse blowing the power cord getting knocked loose the UPS shutting down before the system does a clean shutdown Having an UPS and wiring it so that the system does a clean shutdown before the UPS shuts down is pretty desirable, but there are enough other common failure modes that can result in a corrupted filesystem if write caching is enabled that I don't feel it's worth the minimal performance gain that I see. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199810141852.LAA19279>