[linux-lvm] Verständnis von Stripes bei LVM

[linux-lvm] Verständnis von Stripes bei LVM

[Pawlowski Julian]

Hallo Heinz!

ich habe eine Frage zur Funktion von Stripes beim LVM. Wofür genau
benötigt man diese Funktion? Wird damit das LV auf mehrere der reellen
Partitionen zwecks Performancegewinn verteilt?

Hoffe auf eine Antwort... ;-)


Gruß

Julian
-- 
SZM Studios GmbH IT-Service . ProSiebenSat.1 Media AG
Julian Pawlowski . mailto:Julian.Pawlowski@szm.de
Gutenbergstraße 3 . 85774 Unterföhring
http://www.szm.de/ . http://www.ProSiebenSat1.com/ 

Re: [linux-lvm] Verst?ndnis von Stripes bei LVM

[Jan-Benedict Glaw]

On Fri, 2001-09-14 11:32:13 +0200, Pawlowski Julian <Julian.Pawlowski@szm.de>
wrote in message <4C45858D148AD411A8B800A024B36E5009F4C994@granada.fhm.de>:

I've translated this German writer's text to be readable by others...



> Hallo Heinz!

Hello Heinz!

> ich habe eine Frage zur Funktion von Stripes beim LVM. Wofür genau

I've got some question wrt the functionallity of stripes. For what

> benötigt man diese Funktion? Wird damit das LV auf mehrere der reellen

exactly do I need them? Is a LV to be distributed over multiple

> Partitionen zwecks Performancegewinn verteilt?

partitions to gain better performance?






MfG, JBG

-- 
Jan-Benedict Glaw . jbglaw@lug-owl.de . +49-172-7608481

[linux-lvm] Re: [linux-lvm] Verständnis von Stripes bei LVM

[Goetz Bock]

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On Fri, Sep 14 '01 at 11:32, Pawlowski Julian wrote:
> ich habe eine Frage zur Funktion von Stripes beim LVM. Wofür genau
> benötigt man diese Funktion? Wird damit das LV auf mehrere der reellen
> Partitionen zwecks Performancegewinn verteilt?
Yes, that's exactly the intended bahaviour. if you have n (e.g. 2 or
more) PV than a striped LV is splitted between this n PV. This can
increase performance (like RIAD0 does) but it may backfire, if your PV
are on the same reald device.
If you want to use striped LVs, only use one PV per real device.

e.g.: 4 HDDs of 40GB each (sda, sdb, sdc, sdd)

you boot from sda and decide to have a 512MB root/boot partition for
this. Than make 3 swap partitiones on sdb, sdc and sdd.

on each device make a seccond partition with the rest of the space.
create a PV out of each of this 4 partitions.

you now have:

sda: sda1    512MB  root/boot
     sda2   39.5GB  PV1
sdb: sdb1    512MB  swap
     sdb2   39.5GB  PV2
sdc: sdc1    512MB  swap
     sdc2   39.5GB  PV3
sdd: sdd1    512MB  swap
     sdd2   39.5GB  PV4

VG1:       118.0GB  PV1 PV2 PV3 PV4

if you now make a striped LV of 20GB it will use 5GB on each PV and the
stripes will be read from PV1 PV2 PV3 PV4 PV1 PV2 PV3 PV4 ...

BTW: if you write your question in english a lot more people will be
     able to send you a reply.

PS: und wenn Du willst kann ich Dir das ganze gerne nochmal auf Deutsch
    schicken.

-- 
Goetz Bock                                              IT Consultant
Dipl.-Inf. Univ.

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Re: [linux-lvm] Re: [linux-lvm] Verständnis von Stripes bei LVM

[svetljo]

it's probably a silly question, but what about

Re: [linux-lvm] diff. in striping between HP-UX and Linux LVM from Heinz 
Mauelshagen

probably it's better to have a linear LV over software RAID-0

Goetz Bock wrote:

>On Fri, Sep 14 '01 at 11:32, Pawlowski Julian wrote:
>
>>ich habe eine Frage zur Funktion von Stripes beim LVM. Wof�r genau
>>ben�tigt man diese Funktion? Wird damit das LV auf mehrere der reellen
>>Partitionen zwecks Performancegewinn verteilt?
>>
>Yes, that's exactly the intended bahaviour. if you have n (e.g. 2 or
>more) PV than a striped LV is splitted between this n PV. This can
>increase performance (like RIAD0 does) but it may backfire, if your PV
>are on the same reald device.
>If you want to use striped LVs, only use one PV per real device.
>
>e.g.: 4 HDDs of 40GB each (sda, sdb, sdc, sdd)
>
>you boot from sda and decide to have a 512MB root/boot partition for
>this. Than make 3 swap partitiones on sdb, sdc and sdd.
>
>on each device make a seccond partition with the rest of the space.
>create a PV out of each of this 4 partitions.
>
>you now have:
>
>sda: sda1    512MB  root/boot
>     sda2   39.5GB  PV1
>sdb: sdb1    512MB  swap
>     sdb2   39.5GB  PV2
>sdc: sdc1    512MB  swap
>     sdc2   39.5GB  PV3
>sdd: sdd1    512MB  swap
>     sdd2   39.5GB  PV4
>
>VG1:       118.0GB  PV1 PV2 PV3 PV4
>
>if you now make a striped LV of 20GB it will use 5GB on each PV and the
>stripes will be read from PV1 PV2 PV3 PV4 PV1 PV2 PV3 PV4 ...
>
>BTW: if you write your question in english a lot more people will be
>     able to send you a reply.
>
>PS: und wenn Du willst kann ich Dir das ganze gerne nochmal auf Deutsch
>    schicken.
>

[linux-lvm] Re: [linux-lvm] Verständnis von Stripes bei LVM

[Heinz J . Mauelshagen]

Julian,

because you asked me directly:
are the other already fiven answers sufficient for you?


On Fri, Sep 14, 2001 at 11:32:13AM +0200, Pawlowski Julian wrote:
> Hallo Heinz!
> 
> ich habe eine Frage zur Funktion von Stripes beim LVM. Wofür genau
> benötigt man diese Funktion? Wird damit das LV auf mehrere der reellen
> Partitionen zwecks Performancegewinn verteilt?
> 
> Hoffe auf eine Antwort... ;-)
> 
> 
> Gruß
> 
> Julian
> -- 
> SZM Studios GmbH IT-Service . ProSiebenSat.1 Media AG
> Julian Pawlowski . mailto:Julian.Pawlowski@szm.de
> Gutenbergstraße 3 . 85774 Unterföhring
> http://www.szm.de/ . http://www.ProSiebenSat1.com/ 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Re: [linux-lvm] Re: =?unknown-8bit?B?W2xp?= =?unknown-8bit?Q?nux-lvm=5D_Verst=E4ndnis?= von Stripes bei LVM

[Andreas Dilger]

On Sep 14, 2001  12:13 +0200, Goetz Bock wrote:
> On Fri, Sep 14 '01 at 11:32, Pawlowski Julian wrote:
> > ich habe eine Frage zur Funktion von Stripes beim LVM. Wof?r genau
> > ben?tigt man diese Funktion? Wird damit das LV auf mehrere der reellen
> > Partitionen zwecks Performancegewinn verteilt?
>
> Yes, that's exactly the intended bahaviour. if you have n (e.g. 2 or
> more) PV than a striped LV is splitted between this n PV. This can
> increase performance (like RIAD0 does) but it may backfire, if your PV
> are on the same reald device.
> If you want to use striped LVs, only use one PV per real device.
> 
> e.g.: 4 HDDs of 40GB each (sda, sdb, sdc, sdd)
> 
> you boot from sda and decide to have a 512MB root/boot partition for
> this. Than make 3 swap partitiones on sdb, sdc and sdd.
> 
> on each device make a seccond partition with the rest of the space.
> create a PV out of each of this 4 partitions.
> 
> you now have:
> 
> sda: sda1    512MB  root/boot
>      sda2   39.5GB  PV1
> sdb: sdb1    512MB  swap
>      sdb2   39.5GB  PV2
> sdc: sdc1    512MB  swap
>      sdc2   39.5GB  PV3
> sdd: sdd1    512MB  swap
>      sdd2   39.5GB  PV4
> 
> VG1:       118.0GB  PV1 PV2 PV3 PV4
> 
> if you now make a striped LV of 20GB it will use 5GB on each PV and the
> stripes will be read from PV1 PV2 PV3 PV4 PV1 PV2 PV3 PV4 ...

A note here - very rarely can one really get the theoretical performance
from striped LVs.  There are several problems with stipes:

- bus bandwidth is often limited, so you often do not get N*disk_bandwidth
- application bandwidth is often limited, so you do not NEED N*disk_bandwidth
- for EACH read from a striped LV, you need to seek all disks to that
  spot, which means you often have to wait for the MAXIMUM seek time
  of all disks.  With non-striped LVs, you can do parallel read/write
  from different parts of the each disk (e.g. /usr, /home, /var, swap)
- if you have problems with ANY disk, you have lost ALL of your data

Cheers, Andreas
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert

[linux-lvm] Re: [linux-lvm] Re: [linux-lvm] Verständnis von Stripes bei LVM

[Goetz Bock]

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> [ ... ] There are several problems with stipes:
> 
> - if you have problems with ANY disk, you have lost ALL of your data
If any disk of my VG dies I'm in trouble. With the help of the LVM guis
I might be able to "fake" the broken disk BUT for most people a broken
disk means loos of all data in the WHOLE VG.

... that's why I use LVM over RAID5 (hardware).
-- 
Goetz Bock                                              IT Consultant
Dipl.-Inf. Univ.

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Re: [linux-lvm] Re: [linux-lvm] Re: [linux-lvm] Verständnis von Stripes bei LVM

[svetljo]

well you could do it with soft RAID-5 too i think
you save some money from the hardware RAID ,
you lose a bit performance -- soft RAID overhead
the hard RAID has RAM and CPU( or smth of the kind ) -- no CPU or mem 
overhead
but if you have a mothern CPU and a bit more RAM there is no problem
redundancy - the same
 

Goetz Bock wrote:

>>[ ... ] There are several problems with stipes:
>>
>>- if you have problems with ANY disk, you have lost ALL of your data
>>
>If any disk of my VG dies I'm in trouble. With the help of the LVM guis
>I might be able to "fake" the broken disk BUT for most people a broken
>disk means loos of all data in the WHOLE VG.
>
>... that's why I use LVM over RAID5 (hardware).
>