[linux-lvm] why do striping and mirroring in LVM?

[linux-lvm] why do striping and mirroring in LVM?

[lilha]

i know that lvm support striping now and LVM2 will support mirroring
directly later this year.
but i'm puzzled that why lvm do that?

i think the main Goals of LVM are
     1.Implement a very flexible virtual disk subsystem to handle disk
storage.
     2.Online allocation and relocation of storage.
     3.Online extension and reduction of storage.
And disk redundancy is the goals of  hardware. or software.RAID.

i think software.RAID+LVM is good idea,and that's enough.
why LVM focus on the striping and mirroring?
i don't think it's a good idea to do a big and full software.

there are any reasons and advantages to use striping or mirroring LVM than
software.RAID+LVM ?

i think the reason is LVM it does not matter where the disks are at all.
We can do the same with two big external storage towers, not just with two
disks.

but i think this reason is not enough, can anyone give me some support?
and how many people use striping or mirroring LVM£¬not software.RAID+LVM£¿


TIA for your help and sorry for my poor English.

Echo

Re: [linux-lvm] why do striping and mirroring in LVM?

[lembark]

-- lilha@legend.com.cn on 06/27/02 10:35:18 +0800

> 
> 
> i know that lvm support striping now and LVM2 will support mirroring
> directly later this year.
> but i'm puzzled that why lvm do that?
> 
> i think the main Goals of LVM are
>      1.Implement a very flexible virtual disk subsystem to handle disk
> storage.
>      2.Online allocation and relocation of storage.
>      3.Online extension and reduction of storage.
> And disk redundancy is the goals of  hardware. or software.RAID.
> 
> i think software.RAID+LVM is good idea,and that's enough.
> why LVM focus on the striping and mirroring?
> i don't think it's a good idea to do a big and full software.
> 

RAID is about fault tolerance. Striping is a performance
issue. Mirroring on LVM or via RAID is about fault tolerance
and maybe performance. 

So... For blind speed you probably want striping, but risk
blowing everyting if any one disk fails. Fix is to use some
sort of RAID/Mirroring to deal with the failures.

You might also want the fault tolerance just for the sake of
not loosing important information if one drive croaks. If 
you are already using LVM and don't want to go through the 
hassle of setting up sorftware RAID (and don't have a few
hundred dollars availble for hardware) then mirroring in LVM
is a nice, clean way to protect yourself using tools you 
already have (and know how to use)(and know how to configure)
(and know how install)(and know how to compile).

Depending on how it's implemented, LVM mirroring can also be
a performance enhancment. For example, HP's LVM system
alternates between the mirrors for writes, allowing the other
drive to catch up. On heavily used systems this will usually
help I/O performance by alternating the load -- it ends up
looking like a form of striping.

--
Steven Lembark                              2930 W. Palmer
Workhorse Computing                      Chicago, IL 60647
                                           +1 800 762 1582

Re: [linux-lvm] why do striping and mirroring in LVM?

[Kirby C. Bohling]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="windows-1254", Size: 2290 bytes --]

Try mucking about with a mirror that has LVM on top of it, and you don't
have enough disk space to do the shuffle.  You can't re-configure any of
the sizes of the mirror when you can't get all the data off the mirror.
 You can't reconfigure the striping without getting all of the data off.
 If the LVM and RAID know about each other, then you can reconfigure
stripes and mirrors without removing all of the devices off of LVM.  You
can do all that, and never take anything offline even.  It's my
understanding that with the HP/UX LVM software you can reconfigure all
of that, and it will work, and it should be consistant across
crashes/reboots and just work.  Having the two know about each other
means you can reconfigure both of them efficently.  Plus it gets rid of
the of the FAQ, why doesn't LVM do mirroring.  I find it very ironic
that now somebody asks why bother supporting mirroring inside of LVM.

	Kirby


lilha@legend.com.cn wrote:
> 
> i know that lvm support striping now and LVM2 will support mirroring
> directly later this year.
> but i'm puzzled that why lvm do that?
> 
> i think the main Goals of LVM are
>      1.Implement a very flexible virtual disk subsystem to handle disk
> storage.
>      2.Online allocation and relocation of storage.
>      3.Online extension and reduction of storage.
> And disk redundancy is the goals of  hardware. or software.RAID.
> 
> i think software.RAID+LVM is good idea,and that's enough.
> why LVM focus on the striping and mirroring?
> i don't think it's a good idea to do a big and full software.
> 
> there are any reasons and advantages to use striping or mirroring LVM than
> software.RAID+LVM ?
> 
> i think the reason is LVM it does not matter where the disks are at all.
> We can do the same with two big external storage towers, not just with two
> disks.
> 
> but i think this reason is not enough, can anyone give me some support?
> and how many people use striping or mirroring LVM£¬not software.RAID+LVM£¿
> 
> 
> TIA for your help and sorry for my poor English.
> 
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Re: [linux-lvm] why do striping and mirroring in LVM?

[Svetoslav Slavtchev]

Quoting lilha@legend.com.cn:

> 
> 
> i know that lvm support striping now and LVM2 will support mirroring
> directly later this year.
> but i'm puzzled that why lvm do that?
> 
> i think the main Goals of LVM are
>      1.Implement a very flexible virtual disk subsystem to handle disk
> storage.
>      2.Online allocation and relocation of storage.
>      3.Online extension and reduction of storage.
> And disk redundancy is the goals of  hardware. or software.RAID.
> 
> i think software.RAID+LVM is good idea,and that's enough.
it's a good idea cause LVM doesn't support mirroring and is not that good at
stripping, and it would be very good if one could use the featchers without
needing other layer ( soft RAID)
> why LVM focus on the striping and mirroring?
i think every other implementation supports them
> i don't think it's a good idea to do a big and full software.
> 
> there are any reasons and advantages to use striping or mirroring LVM
> than
> software.RAID+LVM ?
useing LVM over soft RAID adds extra overhead,  is more CPU intensive

> i think the reason is LVM it does not matter where the disks are at
> all.
> We can do the same with two big external storage towers, not just with
> two
> disks.
> 
> but i think this reason is not enough, can anyone give me some support?
> and how many people use striping or mirroring LVM��not
> software.RAID+LVM��
> 
> 
> TIA for your help and sorry for my poor English.
> 
>