-- Steve Wray <steve.wray@the.net.nz> >> From: linux-lvm-admin@sistina.com [mailto:linux-lvm-admin@sistina.com]On >> Behalf Of Bradley M Alexander >> On Fri, Nov 23, 2001 at 05:32:07PM +1300, Steve Wray wrote: >> > >> > thats dead right; ide can't simultaneously write to the master and >> > slave on the same controller. Also, the pair of drives uses the >> > controller circuitry >> > of the master, so it always pays to make the master the most modern >> > one. >> >> Since both controllers have a drive master and a cd slave, this shouldn't >> matter, per se. > > yeah but I thought I'd mention it, for completeness > :) Dependong on the bios, for example, there still could be contention on the SB chipset for access to the controllers. Point is that there can be multiple bottlenecks. >> > > Can anyone give me any ideas as to why the machine gets >> beaten about so >> > > much during IO operations and more importantly how can I minimize the >> > > impact. >> > >> > Dunno, if it was because the fs is striped across those drives then >> > splitting them across controllers would have made it go away. >> >> Nothing should be striped across the drives. I have two PVs and made two >> VGs, one on each drive. The way it works out, the data I am >> mastering is on > > yup you have to tell it to stripe, as I recall. Never used that feature > tho. I'm using LVM with several striped volumes. Hardware is Tekram 160MB scsi + pair of 80MB drives. The striping works rather nicely: sustained I/O is high for large copies and latency is low for reads. The file system uses a 4KB page w/ the inodes reduced to a reasonable value (e.g., mkfs.ext2 -b4096 -i10240). If you are using the default of 1block / page then it can hammer a system due to 2ndary access and higher write rate. >> > I've seen no performance problems at all and really thrashed an >> > LVM-root machine for test purposes while working on a movie. It took >> > it well, performance-wise. (reliability is another issue; never go >> > LVM-root... but thats just my 2 cents, YMMV). >> >> Yeah, I wasn't brave enough to go all out...And with the problems I was >> having, I'm glad I made that decision. :) > > I think the worst part is the lack of backward compatibility > at some stages of LVM. With root on LVM it can be a bit dangerous > to upgrade! Or at least it was... <broken-record> This can also be a real pain to fix if something goes wrong. If the lvm is --prefix-ed to, say, /lvm and the root volume is on a paritition then you can fix most things w/o having to play with rescue file systems. </broken-record> -- Steven Lembark 2930 W. Palmer Workhorse Computing Chicago, IL 60647 +1 800 762 1582
