Date: Thu, 7 Mar 2002 20:18:42 -0600 From: "Mike Meyer" <mwm-dated-1015985923.090d92@mired.org> To: "Hartmann, O." <ohartman@klima.physik.uni-mainz.de> Cc: questions@freebsd.org Subject: Re: mount option 'ASYNC' on UFS filesystems? Message-ID: <15496.8066.447539.220015@guru.mired.org> In-Reply-To: <133394040@toto.iv>
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Hartmann, O. <ohartman@klima.physik.uni-mainz.de> types: > Dear Sirs. > > It is said that it could be very dangerous enabling the option > 'async' in /etc/fstab on each mounted UFS filesystem. I can > follow this warning so far as I'm on a normal IDE/SCSI type > device, but what's about a RAID 5? It's still true for RAID 5. > I wish to enable this option on several server based file systems > located on a RAID 5 controller (AMI Enterprise 1600 RAID, battery > backed up cache memory). Due to the fact that the controller uses > a battery backed up cache likelyhood of crash and data loss seems > to be small, but just in case all buffers are written to the controller's > memory and there are no remains in the system memory space. The problem with async is that you have no guarantee that what's in the controller's memory at any given time is a valid file system. So all your battery backup means is that your broken file system is safely written to the disk. Not a very comforting thought, is it? > Can anyone give some hints, tips or comments about that? Yes. Don't use async. Use softupdates; they are almost as fast async, and will guarantee that the data in your controllers memory is a valid file system structure. You can still lose data, but at least your file system will be valid. If you want the best integrity you can get, use SYNC instead of the default. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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