From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <3AC61117.F16884CD@tnonline.net> Date: Sat, 31 Mar 2001 19:17:11 +0200 From: Anders Widman MIME-Version: 1.0 Subject: Re: [linux-lvm] LVM and fault tolerance References: <20010327235600.H20535@vestdata.no> <3AC1142D.C47A9C96@tnonline.net> <0103281643400K.27902@lyta> Content-Transfer-Encoding: 7bit Sender: linux-lvm-admin@sistina.com Errors-To: linux-lvm-admin@sistina.com Reply-To: linux-lvm@sistina.com List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@sistina.com Well. Yes. The ideal way is of course to buy more 80GB disks. So, there is no way that linux does support rebuilding an RAID 4/5 array when adding extra disks (of equal size)? Thanks, Anders Russell Coker wrote: > On Wednesday 28 March 2001 08:29, Anders Widman wrote: > > ok. great... so if I make say 20GB partitions on all disks and put them > > in a RAID-5 array. Can I add extra disks and rebuild the array? I have > > seen some expensive RAID cards that does that. > > RAID-4 involves having N data disks (N >= 2) and 1 parity disk. The parity > disk contains the XOR of the blocks on the N data disks. If one of the N > disks dies then it's contents can easily be regenerated by the XOR of the > surviving N-1 disks and the parity disk. > RAID-5 is the same but has the parity data spread across all the disks for > best performance. Thus RAID-5 has 3 or more disks. > > In RAID-4 or RAID-5 if you lose two disks at the same time then the XOR won't > get your data back and you are comprehensively stuffed. > > If you create a RAID-5 with two partitions on the same disk then you may as > well use a bulk eraser. > > The scheme I mentioned in my previous message is the simplest way of doing > this with such disks. But really if your time is worth more than about $10 > per hour you should just buy some more 80G disks. > > -- > http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark > http://www.coker.com.au/postal/ Postal SMTP/POP benchmark > http://www.coker.com.au/projects.html Projects I am working on > http://www.coker.com.au/~russell/ My home page > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm Russell Coker wrote: > On Wednesday 28 March 2001 08:29, Anders Widman wrote: > > ok. great... so if I make say 20GB partitions on all disks and put them > > in a RAID-5 array. Can I add extra disks and rebuild the array? I have > > seen some expensive RAID cards that does that. > > RAID-4 involves having N data disks (N >= 2) and 1 parity disk. The parity > disk contains the XOR of the blocks on the N data disks. If one of the N > disks dies then it's contents can easily be regenerated by the XOR of the > surviving N-1 disks and the parity disk. > RAID-5 is the same but has the parity data spread across all the disks for > best performance. Thus RAID-5 has 3 or more disks. > > In RAID-4 or RAID-5 if you lose two disks at the same time then the XOR won't > get your data back and you are comprehensively stuffed. > > If you create a RAID-5 with two partitions on the same disk then you may as > well use a bulk eraser. > > The scheme I mentioned in my previous message is the simplest way of doing > this with such disks. But really if your time is worth more than about $10 > per hour you should just buy some more 80G disks. > > -- > http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark > http://www.coker.com.au/postal/ Postal SMTP/POP benchmark > http://www.coker.com.au/projects.html Projects I am working on > http://www.coker.com.au/~russell/ My home page > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm Russell Coker wrote: > On Wednesday 28 March 2001 08:29, Anders Widman wrote: > > ok. great... so if I make say 20GB partitions on all disks and put them > > in a RAID-5 array. Can I add extra disks and rebuild the array? I have > > seen some expensive RAID cards that does that. > > RAID-4 involves having N data disks (N >= 2) and 1 parity disk. The parity > disk contains the XOR of the blocks on the N data disks. If one of the N > disks dies then it's contents can easily be regenerated by the XOR of the > surviving N-1 disks and the parity disk. > RAID-5 is the same but has the parity data spread across all the disks for > best performance. Thus RAID-5 has 3 or more disks. > > In RAID-4 or RAID-5 if you lose two disks at the same time then the XOR won't > get your data back and you are comprehensively stuffed. > > If you create a RAID-5 with two partitions on the same disk then you may as > well use a bulk eraser. > > The scheme I mentioned in my previous message is the simplest way of doing > this with such disks. But really if your time is worth more than about $10 > per hour you should just buy some more 80G disks. > > -- > http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark > http://www.coker.com.au/postal/ Postal SMTP/POP benchmark > http://www.coker.com.au/projects.html Projects I am working on > http://www.coker.com.au/~russell/ My home page > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm Russell Coker wrote: > On Wednesday 28 March 2001 08:29, Anders Widman wrote: > > ok. great... so if I make say 20GB partitions on all disks and put them > > in a RAID-5 array. Can I add extra disks and rebuild the array? I have > > seen some expensive RAID cards that does that. > > RAID-4 involves having N data disks (N >= 2) and 1 parity disk. The parity > disk contains the XOR of the blocks on the N data disks. If one of the N > disks dies then it's contents can easily be regenerated by the XOR of the > surviving N-1 disks and the parity disk. > RAID-5 is the same but has the parity data spread across all the disks for > best performance. Thus RAID-5 has 3 or more disks. > > In RAID-4 or RAID-5 if you lose two disks at the same time then the XOR won't > get your data back and you are comprehensively stuffed. > > If you create a RAID-5 with two partitions on the same disk then you may as > well use a bulk eraser. > > The scheme I mentioned in my previous message is the simplest way of doing > this with such disks. But really if your time is worth more than about $10 > per hour you should just buy some more 80G disks. > > -- > http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark > http://www.coker.com.au/postal/ Postal SMTP/POP benchmark > http://www.coker.com.au/projects.html Projects I am working on > http://www.coker.com.au/~russell/ My home page > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm Russell Coker wrote: > On Wednesday 28 March 2001 08:29, Anders Widman wrote: > > ok. great... so if I make say 20GB partitions on all disks and put them > > in a RAID-5 array. Can I add extra disks and rebuild the array? I have > > seen some expensive RAID cards that does that. > > RAID-4 involves having N data disks (N >= 2) and 1 parity disk. The parity > disk contains the XOR of the blocks on the N data disks. If one of the N > disks dies then it's contents can easily be regenerated by the XOR of the > surviving N-1 disks and the parity disk. > RAID-5 is the same but has the parity data spread across all the disks for > best performance. Thus RAID-5 has 3 or more disks. > > In RAID-4 or RAID-5 if you lose two disks at the same time then the XOR won't > get your data back and you are comprehensively stuffed. > > If you create a RAID-5 with two partitions on the same disk then you may as > well use a bulk eraser. > > The scheme I mentioned in my previous message is the simplest way of doing > this with such disks. But really if your time is worth more than about $10 > per hour you should just buy some more 80G disks. > > -- > http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark > http://www.coker.com.au/postal/ Postal SMTP/POP benchmark > http://www.coker.com.au/projects.html Projects I am working on > http://www.coker.com.au/~russell/ My home page > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm