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Re: [linux-lvm] LVM and fault tolerance



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



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