LUN Vs LVM
 

Hello all;

I have a confusion.

Is LUN same as LVM ?

They are both three-letter acronyms that begin with "L". Beyond that, they don't have much in common. Why don't you actually look up both and then indicate what in those descriptions confuses you?

http://www.acronymfinder.com/

LUN = Logical unit
This is usually device presented to the OS as if it were physical disk but is in fact a logical disk (e.g. a RAID device comprised of multiple physical disks). Examples of LUNs would be those provided via SAN to your host from a disk array like those made by Hitachi, EMC, etc... or RAID sets prevented by an internal adapter such as the Dell PERC card.

LVM = Logical Volume Manager
This is a method of combining storage items and subdividing them. Often in large environments like the one here we use LUNs as LVM PVs (Physical Volumes) to create VGs (Volume Groups) that are then subdivided into LVs (Logical Volumes).

So in general when you think of it:
LUN = Something the OS sees as a disk that can be used as a disk in and of itself (i.e. can be partitioned) or combined into other structures such LVs.
LV = A subdivision of another structure called a VG.

Hi MensaWater

Sorry for delay. Thanks for reply.

I Found defination of LUN as below

1) I know what is RAID , what do they mean about Raid controller ?


I seen many inks - they did not use any 3rd volume managers and done LUN configuration.

2. Do we need 3rd party voulme managers to create LUN in SAN storage ?
3. In real env, are they using which controller (scsi/iscsi/fc/sas/) ?

FYI: Few things i dont understand. Example -(internal adapter such as the Dell PERC card)

Simple definition would be better instead of using some terminologies related to STORAGE
I am a beginner :study: thats why i ask real time gurus :jawa: Please dont mind it. :cool:

1. RAID Controller is a generic term that is talking about a hardware adapter in your system that is used to create one or more RAID sets. It can do this for internal disks attached to it or for some external enclosures of disks. It implies "Hardware RAID".

Another type of RAID is "Software RAID" which is when you use software to create RAID sets rather than a controller. Examples of this would be Linux Meta-disks and Veritas Volume Manager (VxVM). LVM itself although not generally thought of as RAID is actually RAID to the degree that it concatenates multiple devices into a VG usually and can also do mirroring (RAID 1). One of the tricky things about storage discussions is you can use entire disks, individual partitions of disks or LUNs presented by other tools within volume managers like LVM and VxVM. (e.g. You could use meta-disks mirors as your PVs within LVM).

VxVM or another commercial software might be what your tutor means by "3rd party volume managers". He may also be talking about an external disk array that presents its own devices (LUNs) to your system.

2. No. If your SAN environment includes an external disk array that presents devices to your operating system (OS) then you can often use those devices the same way you would any internal disk. The devices you see are LUNs but your system just sees them as disks.
However, many of the large array makers may have tools you can install on the OS to manage disks. (e.g. EMC provides PowerPath for multipathing which can be used instead of the native Linux multipathd. Other tools such as VxVM have things such as Dynamic Multipath [DMP] that can be used. Often if you're using SAN you do want to do multipathing of some sort to prevent single points of failure and/or to increase througput.

3. In real environments people may use any or all of the technologies. For examaple here we use Dell PERC in our Dell Servers to create hardware RAID on internal disks but also use Qlogic fiber channel (FC) controllers to present disks from external arrays (previously EMC and now Hitachi) to our servers for additional storage requirements such as that needed by large databases. Generally speaking we put all devices in VGs that we subdivide into LVs as required.
Your "scsi/iscsi/fc/sas" is mixing concepts:
SAS = Serial attached SCSI but is usually used to refer to a type of disk and the way it connects to whatever it is installed in (e.g. servers can have internal SAS drives and disk arrays can also contain SAS drives). Most of the newer PERC controllers are actually SAS controllers that let you build RAID on the attached SAS drives.
SCSI = A type of disk and also a type of attachment that predates SAS. FC actually presents disks over SCSI.
FC = Fibre channel - A type of SAN attachment that uses SCSI standards to present disks over fibre optics. However, there are hybrid solutions such as FCOE which does "fibre channel over ethernet".
iSCSI = Using normal networking hardware to present storage using SCSI protocols. Some disk arrays have both FC and iSCSI built in. Note this is a competing (and more often used) standard to FCOE.
You didn't mention SATA/PATA/IDE which is another disk type and attachment.
Just to make it fun SCSI connections themselves can be varied.

Asking for simple definitions of complex subjects isn't going to get you anywhere. I *did* give you simple definitions followed by discussion. As you can see from the above you are actually asking about multiple different things under an overall concept called "storage" which is a very broad category. You can search the web for any concept followed by the word tutorial.
e.g.
scsi tutorial
sas tutorial
fc tutorial
raid tutorial
lvm tutorial
san tutorial

Attempting to understand everything all at once isn't usually a good strategy. I find learning concepts as I need to use them works much better.

Thanks MensaWater.

Also if you want to readup on LVM and how to use it here are some URLS that helped me.

http://www.howtogeek.com/howto/40702...ent-in-ubuntu/

http://blog.frands.net/linux-lvm-how-to-182/