That's basically what I gathered from what I had been reading also... is there any way to "defrag" so to speak the data, so say I end up deleting data from 300mb of PE's on disk1 then when I write 600mb or data, I don't want 300mb to go to disk1 and 300mb to disk2 cause after any bit of time has passed on a fairly used system it will no longer really be linear at all! I guess I'm asking a lot for this system :( Cheap is a relative term ;) I just got the two 80gigs and only because there was a $60 rebate on each of them from Bestbuy so I got to fudge one of my rebate forms to be sent to someone else to get my $120 for both drives ;) ----- Original Message ----- From: "Clint Byrum" <cbyrum@spamaps.org> To: "LVM general discussion and development" <linux-lvm@redhat.com> Sent: Friday, November 05, 2004 5:37 PM Subject: Re: How exactly does LVM's get written? > On Fri, 2004-11-05 at 17:16 -0600, Kevin Richard wrote: > > I have searched many topics in archive and even randomly scanned for any > > info related to this but have only come away with a "I think it works this > > way" feeling. > > > > I set up two 80gig drives as one 160gig VG /dev/VG1/LV1 I then proceeded > > to copy about 93 gigs of data from a 100gig drive that I will hopefully add > > to the LV to make it 260gigs. > > > > My questions are: > > > > 1. Is this a "spill over" type of write method where it will fill up hde1 > > (first 80gig) and then move to hdf1 (other 80gig) and then of coarse on to > > hdg1 (100gig)? Which would allow me the convenience of having one HUGE > > mount and thus not having to constantly monitor and move data to 3 different > > drives as space is needed. Yet it keeps the data somewhat separated (except > > for the "spill over" that might get wrote to two drives at some point) so if > > I lose a hard drive I only lose what is on that drive and can just replace > > the drive and recreate the VG and salvage all the data on the other two > > drives. Is this a correct assumption? I am trying to avoid the disaster of > > a Raid 0 type of system where if you lose one drive you have lost all 3 > > drives! > > > > I'm no LVM expert, but I see this question a lot. I think its because of > a misunderstanding of the seperation of filesystem from block device. > > Each volume group has a number of physical volumes in it. When you add a > logical volume, the PE's in each PV are allocated in a pretty much > linear fashion, unless you specify striping. So if you allocate 90G from > your original 160G VG, you'll get 80G on the first disk, and then 10G > from the second. The idea behind LVM is that you don't care which drives > the PE's come from, they're just there and available with your data on > them. > > > 2. Is there any way to tell what PE's contain what data? or to see how the > > volumes are filling up? This would essentially allow me to answer my own > > first question and also verify that it is doing as I want it to do. To > > clarify, I would be able to tell that Datafile.X which is a 1gig file is > > written to PE's stored on hde1 or hde1 AND hdf1. > > > > My first inclination would be "no". LVM thinks the PE's are "filled" > when they're allocated. It doesn't really care what is writing to each > PE, and whether or not its data, journal, new filesystem, etc. > > This is why I personally think its a really bad idea to use LVM without > some sort of disk redundancy. Even if "I can lose the data and it won't > matter", how much is your time worth? They're so darn cheap now... just > use RAID5 and you'll be much happier. > > -- > Clint Byrum <cbyrum@spamaps.org> > > _______________________________________________ > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
