I've been reading the RHEL 5 manual/guide linked from centos, and the idea of LVM with expandable partitions seems like a great idea (yes duh why else would it exist if not?). Although the documentation shows a screenshot of how the final setup would look like with LVM & RAID together, it doesn't actually gives the step.
1. Am I correct in thinking it should be done in this way - setup Softraid - setup LVM on the raid partitions
Secondly, LVM allows expansion of the LVM group when we add a new drive. But with softraid, how will this happen? Searching around does not turn up any guide on this. Am I correct in thinking I must always add new drives in pairs (for Raid 1), create a new softraid partition then assign this new partition to the LVM group?
Thanks!
Cen Tos wrote:
I've been reading the RHEL 5 manual/guide linked from centos, and the idea of LVM with expandable partitions seems like a great idea (yes duh why else would it exist if not?). Although the documentation shows a screenshot of how the final setup would look like with LVM & RAID together, it doesn't actually gives the step.
- Am I correct in thinking it should be done in this way
- setup Softraid
- setup LVM on the raid partitions
Secondly, LVM allows expansion of the LVM group when we add a new drive. But with softraid, how will this happen? Searching around does not turn up any guide on this. Am I correct in thinking I must always add new drives in pairs (for Raid 1), create a new softraid partition then assign this new partition to the LVM group?
yup, pretty much thats how it works.
In IBM AIX (where LVM kinda came from), the soft raid and volume management is rather tightly integrated, but in linux, its seperate.
On Sat, 2007-03-31 at 22:14 -0700, John R Pierce wrote:
Cen Tos wrote:
I've been reading the RHEL 5 manual/guide linked from centos, and the idea of LVM with expandable partitions seems like a great idea (yes duh why else would it exist if not?). Although the documentation shows a screenshot of how the final setup would look like with LVM & RAID together, it doesn't actually gives the step.
- Am I correct in thinking it should be done in this way
- setup Softraid
- setup LVM on the raid partitions
Secondly, LVM allows expansion of the LVM group when we add a new drive. But with softraid, how will this happen? Searching around does not turn up any guide on this. Am I correct in thinking I must always add new drives in pairs (for Raid 1), create a new softraid partition then assign this new partition to the LVM group?
yup, pretty much thats how it works.
In IBM AIX (where LVM kinda came from), the soft raid and volume management is rather tightly integrated, but in linux, its seperate.
I guess you've got the gist of the matter right - setup software raid - setup LVM on the software raid paritions
and if you need to increase space thereafter - add in the physical drives - setup new software raid - add these /dev/mdX into LVM (pvcreate, vgextend etc.)
John R Pierce wrote:
In IBM AIX (where LVM kinda came from), the soft raid and volume management is rather tightly integrated, but in linux, its seperate.
There is not RAID in AIX LVM, just mirroring (well, stripes too but never mind that). Since you just map Logical Partitions to multiple Physical Partitions (same as Physical Extents, PE, in the linux implementation), it is easy to duplicate logical volumes to different physical volumes. You can do this online of course, as it is all below the filesystem/logical volume level. Migrating from one SAN to another, one disk to another, adding disks, splitting disks, removing disks. All is done in the LVM. As it should be.
The linux approach is much more primitive. Too bad the linux lvm guys used HP-UX LVM as their reference.
There is not RAID in AIX LVM, just mirroring (well, stripes too but never mind that). Since you just map Logical Partitions to multiple Physical Partitions (same as Physical Extents, PE, in the linux implementation), it is easy to duplicate logical volumes to different physical volumes. You can do this online of course, as it is all below the filesystem/logical volume level. Migrating from one SAN to another, one disk to another, adding disks, splitting disks, removing disks. All is done in the LVM. As it should be.
The linux approach is much more primitive. Too bad the linux lvm guys used HP-UX LVM as their reference.
http://www.catb.org/~esr/hackerlore/sco-vs-ibm.html
to quote:
logical volume management (LVM)
It is a matter of record [53] that IBM's approach to LVM was rejected by Linus Torvalds in favor of a different approach. Accordingly, even if we were to stipulate that IBM had access to old SCO's LVM technology, any attempted misappropriation came to naught.
Thad
thad wrote:
It is a matter of record [53] that IBM's approach to LVM was rejected by Linus Torvalds in favor of a different approach. Accordingly, even if we were to stipulate that IBM had access to old SCO's LVM technology, any attempted misappropriation came to naught.
That was a different matter; EVMS vs LVM. And even there Linus was and is wrong. The Linux implementation is "good enough" and linux as an OS can probably live with it. It is just a little sad that "good enough" is enough sometimes, esp. when the alternative is not harder to implement.
But this is getting pretty off-topic.
On 4/1/07, Morten Torstensen morten@mortent.org wrote:
John R Pierce wrote:
In IBM AIX (where LVM kinda came from), the soft raid and volume management is rather tightly integrated, but in linux, its seperate.
There is not RAID in AIX LVM, just mirroring (well, stripes too but never mind that). Since you just map Logical Partitions to multiple Physical Partitions (same as Physical Extents, PE, in the linux implementation), it is easy to duplicate logical volumes to different physical volumes. You can do this online of course, as it is all below the filesystem/logical volume level. Migrating from one SAN to another, one disk to another, adding disks, splitting disks, removing disks. All is done in the LVM. As it should be.
The linux approach is much more primitive. Too bad the linux lvm guys used HP-UX LVM as their reference.
Used to manage HP/UX systems (eons ago) and raid was integrated into their LVM implementation also.
Cheers..james
I haven't evaluated centos 5 beta yet, so I don't know what its kernel supports. 'The' linux kernel supports resizing (grow only) of softraid 5 arrays. Combine that with LVM2, which supports hot-growth and a file-system that supports some sort of growth (I'm using xfs), and you have a very flexible and expandable configuration.
I'm not so sure you "need" to resize a raid 5 array with lvm, but it makes expanding the storage cheaper. Without resize, to expand you need to buy enough drives to form a new array, define it as a PV and extend one or more VGs to it. With hot grow, you just add one (or more) drives, resize the array and expand the underlying PV (and VGs)..
Maybe someone else has a simpler method? This looks like a lot when you write it out, but its just two or three commands and a lot of patience.
Gordon
On 4/1/07, Cen Tos centos.admin@gmail.com wrote:
I've been reading the RHEL 5 manual/guide linked from centos, and the idea of LVM with expandable partitions seems like a great idea (yes duh why else would it exist if not?). Although the documentation shows a screenshot of how the final setup would look like with LVM & RAID together, it doesn't actually gives the step.
- Am I correct in thinking it should be done in this way
- setup Softraid
- setup LVM on the raid partitions
Secondly, LVM allows expansion of the LVM group when we add a new drive. But with softraid, how will this happen? Searching around does not turn up any guide on this. Am I correct in thinking I must always add new drives in pairs (for Raid 1), create a new softraid partition then assign this new partition to the LVM group?
Thanks!
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