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Old 05-26-2006, 09:45 AM   #1
CleonII
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Technical question. (related to striping) (Symmetrix question)


Hi all,
I have a technical question.
Could be usefull create a striped Logical Volume if the disks where its going to reside are storage striped disks? this is a redundance? or could improbe performance? or its downgrading the performance?

thanks to all in advanced.

Last edited by CleonII; 05-27-2006 at 11:35 AM.
 
Old 05-26-2006, 09:59 AM   #2
KarlosDaJackel
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Clarify please.

It cant be redundant as a stipe is never redundant. Your thinking of mirroring.

Software raid on top of hardware raid is a bad idea (twice as complex, harder to manage, twice the potential to fail)

Is it a hardware base raid card? What are you aiming for speed/redundancy/both?
 
Old 05-26-2006, 10:09 AM   #3
CleonII
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Karlos, Thanks for your quick answer.
I think maybe i was not too clear. Im going to explain it a little better.
I have a HP-UX server, that is connected to a Symmetrix. Symmetrix is a Storage box.
I have a lot of disks from this symmetrix in this server. The symmetrix strips the disks but this stripping is transparent for the server.
i added 4 disks (of this Symmetrix disks) into a Volume Group and i created a striped LV (striped among the 4 disk).
this is redundant? this improves the perf? this degrades the perf?

thats my question

regards
 
Old 05-26-2006, 11:02 AM   #4
J.W.
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The purpose of disk striping is to improve performance. The basic idea is to take a large chunck of data, divide it into smaller pieces, then physically places those pieces (eg, the stripes) on different hard drives. The intended benefit of such an approach is that while one user is accessing data stored in one area, another user can access data in another area without interference from the first user.

To use an analogy, consider a giant 2 liter bottle of soda vs a six pack of soda. If you've got 6 people who all want a drink, which option will be the fastest way to deliver the soda? Using the large bottle will require that eveyone wait their turns till the bottle comes around to them, but with the six pack, everyone can get their drink at the same time. It's not the best analogy, but hopefully you get the idea.
 
Old 05-26-2006, 05:11 PM   #5
CleonII
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J.W. tanks for your answer too.
But ive already know the advantages of striping. Please read carefully my post, thats not what im asking.

Thanks anyway

regards
 
Old 05-27-2006, 04:19 AM   #6
KarlosDaJackel
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Quote:
Originally Posted by CleonII
Karlos, Thanks for your quick answer.
I think maybe i was not too clear. Im going to explain it a little better.
I have a HP-UX server, that is connected to a Symmetrix. Symmetrix is a Storage box.
I have a lot of disks from this symmetrix in this server. The symmetrix strips the disks but this stripping is transparent for the server.
i added 4 disks (of this Symmetrix disks) into a Volume Group and i created a striped LV (striped among the 4 disk).
this is redundant? this improves the perf? this degrades the perf?

thats my question

regards
I think I get you now
If the disks are in the HP server, and the server does not have a hardware raid controller. You will see the disks as individiuals (e.g. sda sdb sdc sdd etc). If you create a LV stripe across these 4 disks, yes you will improve performace with the risk that if 1 disk fails you loose data on all 4 disks.

I'm a little suprised that the server does not have harddware based raid. If this was the case you would usualy go into the raid bios and setup a raid0 across the 4 disks. This would be presented to the os as a single disk (sda). Then LVM etc would have no bearing on performace. This would be slightly faster also as the OS does not have to do as much work.

Note: If the disks in the symmetrix box are all visible to the operating system as separate entities (sda sdb sdc etc) then the symmetrix box is not striping them at a hardware level.

Do you know what scsi/fiber card the symetrix box is attached to in the server?

Hope this was helpful.
 
Old 05-27-2006, 11:34 AM   #7
CleonII
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Hey Karlos, thanks again.
Do you know the SAN (Storage area network)? This symmetrix its a box connected by fiber channel to my server and many other servers too. This box serves LUNs (they are disks for the OS) and i see 4 LUNs (again, 4 disks for the OS) and i see them as separate disks. But in the Symmetrix, they are not necesarially 4 separate disks, the symmetrix present this disks as common disks for my, but internally, each one of this disks, are commposed of 4 stripped disks. And for my OS, this stripping is invisible.. i just see them as 4 normal disks.
I create a LV stripped among this 4, and thats all.
My doubt is if this Strippes could finally, be in the same disk inside the SYmmetrix, because if they are stripped already inside the Symm maybe 2 diferrent stripes for my OS are located in the same disk in the SYmm and that could cause a loose of performance.
So i think maybe this question is for a Symmetrix expertise..

regards
 
Old 05-28-2006, 11:05 AM   #8
KarlosDaJackel
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Yea I know SAN. But i'm more familiar with the Dell/EMC setup.

Your right to ask symetrix as theres always weird and wonderful ways of doing things with this hardware. I would'nt install the OS onto the SAN! If you end up replacing a server and its os is on the SAN then you have to take risks formating disks on the SAN etc, etc.

Use the SAN for your data and do a mirror on the servers. Of course also backup the servers onto the san. But thats just how I'd do it on the Dell/EMC stuff.

Good luck with symetrix
 
  


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