Regarding RAID 5 in LVM

[Kavita Poonia]

Hello all,

Can we create a RAID-5 FileSystem in LVM on HP-UX server ?

Thanks & regards,
Kavita

[Patrick Wallek · Accepted solution]

Software based RAID 5 is not support in LVM on HP-UX.

I **think** it can be done via Veritas Volume Manager which is an add-on product to HP-UX.

[melvyn burnard]

LVM does not do software raid 5
If you buy the ad-on licenses for VxVM, you can do that, but why not rather use hardware raid, i.e. a raid array?

[Bill Hassell]

RAID-5 in software is very CPU intensive and slows an already very slow RAID level. Most people that try it (VxVM has a RAID-5 module) stop using it unless disk performance is of no concern.

[Lijeesh N G_1]

Hi,

==>LVM will not support RAID-5.
==>For redundancy view, we can do RAID 1 using LVM.
==>VxVM will support RAID 5 if you purchase full version of VxVM;I mean license.
==>You can do RAID 5 in Hardware LEVEL as well,that would be a better option.

Regards,
LIJEESH N G

[SoorajCleris]

Hi Kavita,

In HP-UX there is no RAID5 with LVM. You may use Veritas Volume Manager (VxVM for this ).

Which is your Server and which is the cotroller you are using?
I think that must be having a RAID5 support.
It is always better to configure RAID5 in your hardware.

If available also, I think the RAID5 in software level will make the system complecated

In Linux there is an option of software RAID 5 (md) not LVM.

Regards,
Sooraj

[Kavita Poonia]

Hello All,

Thanks for your replies....but I have one more query here. What do you mean by configuring RAID at software level and at hardware level i.e. hardware RAID ? I am not fully clear with this perspective.

Thanks & regards,
Kavita

[SoorajCleris]

Hi,

Yes. Hardware RAID.

The storage controllers ( which has RAID option) will allow you to create Hardware RAID. In this case for example if you create a RAID1 in the controller and if you have 2* 73GB HDD, it will give a RAID volume of 73GB to the OS (as RAID one is mirroring will give 50%).

OS will not be knowing what is happening behind and controller will manage to write to both disk when there is an operation. If your one of the disk is failed still OS will not know one disk is failed.

In case of software RAID, OS is controlled everything, as far as the OS is available RAID is available. else you will not be able to access anything.

Regards,
Sooraj

[SoorajCleris]

Hi

Probalbly you may refer this page also ..

http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/custom-guide/s1-raid-approaches.html

http://blog.taragana.com/index.php/archive/which-one-is-better-software-raid-or-hardware-raid/

Regards,
Sooraj

[melvyn burnard]

Software RAID is as it's name implies, you install software onto the server to create and manage the RAID5 environment, as in VxVM.
This means your SERVER is using processing power, memory and I/O to control and use the RAID5 infrastructure, in other words, uses capacity on you host.

Hardware Raid, is domne in hardware, such as an XP or EMC array, where the management and contorl of the RAID5 infrastructure is left to the Array Hardware, and hence frees up the server and OS from taking care of that!.

Basically, software RAID is done using server and OS, Hardware RAID is done using array hardware and technology.

[Shailendran V Naidu]

RAID-5 in LVM ......

How many times have I thought about that one !?
Couple of Hundred.

Answer is No.


Even for a plain striping we use PVGs and all the crazy stuff .. !!

[Lijeesh N G_1]

Hi,

Hardware RAID
================
>>By the name itself indicates that we are performing at Hardware level.
>>There is a controller(some time it will be on board or additional PCI card)called RAID controller which will provide this RAID solution.
>>We will create 1st RAID through RAID controller and will present to the OS as a single disk.RAID might be contains more than one disk,but OS will not be knowing that.If you take RAID5 at hardware level, it contains atleast 3 disks(or more),but from OS view it would be a single disk or LUN.

>>Failure of the RAID disk does not effect or no need to recover from OS,ie,Its not managing from OS at all.

Software RAID
===============
>>By the name itself indicates that we are performing at Software leve,ie OS level through some Disk management utilities(LVM,VxVM,etc.).
>>In this case OS will be managing the RAID,failure of the Managing utilities will effect the OS.


Generally we can say that,
Hardware RAID is hidden from OS and Software RAID is hidden from Hardware.

You may check following links for comparison,advantages,etc between them,

http://www.meganet1.com/pdf/Comparing%20Hardware%20vs%20software%20RAID.pdf

http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/custom-guide/s1-raid-approaches.html

http://articles.techrepublic.com.com/5100-10878_11-5715216.html

Regards,
LIJEESH N G

[Bill Hassell]

RAID (Redundant Array of Inex[pensive Disks) is a broad term and comes in simple mirroring (RAID 1), striping (RAID 0), striped with interleaved or distributed parity (RAID 5) and others...See http://en.wikipedia.org/wiki/RAID

RAID 0 is a performance enhancer but no redundancy so all disks are available for storage. RAID 1 is simple mirroring so usable capacity is only half but if one fails, the system can continue using the other disk. RAID 0 and RAID 1 are standard features for LVM.

RAID 5 is very complex. It provides redundancy with a higher amount of usable storage. For example, 5 disks will provide 4 disk worth of storage. Any one disk can fail and the system will still see all the data. This is accomplished by computing and storing checksums that are stored across all the disks. This occurs when the data is first written. When data is read back, the checksums are verified as to the integrity of the data before sending the data to the host.

Additionally, software RAID 5 is severely compromised if any of the disks share the same disk interface. Compromised means that a single controller (with multiple disks) failure disables all the disks since RAID 5 cannot handle more than one disk failure at the time. And since a write must write to all the disks at the same time, a shared controller will be a severe bottleneck for performance.

So software RAID 5 is mostly a novelty. The cost to install extra controllers and the CPU load make it impractical.

Hardware RAID means that all of this special code plus separate buses for each drive are handled inside the RAID box.

[Kavita Poonia]

Thanks a lot for all the replies....now I am very much clear with the concept :)

Thanks & regards,
Kavita