[linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[John Hughes]

                if (lp->stripes > 1) {
                        log_error("mirrors and stripes are currently "
                                  "incompatible");
                        return 0;
                }

Should I just stick with mdadm for my mirroring and striping needs?

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Axel Werner]

Why you need RAID 10 at all ?

Usualy because the need of performance and additional redundancy/fault 
tollerance.
So if u need performance a "Software RAID Solution" would always be a 
bad choice. If you need some sort of redundancy and no performance, go 
for it. if u need performance youll better get yourself a real HARDWARE 
RAID CONTROLLER for your drives. Those cost a bit. but are worth it.

Best RAID Controllers around i do know are those from ICP VORTEX 
(meanwhile belongs to Adaptec). Best Linux Support ever! Accustic alarm, 
SNMP, GUI, CLI Interfaces and Text-oriented tools to handle/configure 
the raid controller within the running os and all.

2nd best are ADAPTEC Raid controllers,

also working good with linux are LSI Logic MEgaRaids. BUT... they dont 
support GNU Linux , only RH Enterprise and Suse Enterprise are 
supported. All software comes within RPM packages. (pretty bullshit!) - 
The only thing that works good is a CLI tool. with some scripting you 
can monitor your drives and raid within the os then. no accustic alarm. 
pretty crappy.

DO NOT USE CHEAP "PSEUDO HARDWARE RAID CONTROLLERS" like DAWI Controll, 
Silicon Chip crap or those other 150$ shity RAID 0 or RAID 1 crap. those 
cheap controllers are NO REAL HARDWARE RAIDs. Those are just simple 
ATA/SATA Adapters with a "more advanced driver". Those Raid controllers 
are NOTHING without their drivers. just a bunch of disks. And that is 
what you usualy can see if you boot a linux on such a controller. even 
if you have configured a RAID5 or RAID1 with only ONE logical drive, 
those controllers will still present ALL physical DRIVES to the OS as 
there would be no RAID configuration at all. Drop those controllers... 
trash em.

Get ICP Vortex (Adaptec) and Adaptec - Those Rock!

greets
Axel



Am 08.04.2009 15:11, John Hughes schrieb:
>                if (lp->stripes > 1) {
>                        log_error("mirrors and stripes are currently "
>                                  "incompatible");
>                        return 0;
>                }
>
> Should I just stick with mdadm for my mirroring and striping needs?
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[John Hughes]

Axel Werner wrote:
> Why you need RAID 10 at all ?
Because my data is important to me, and I need it quickly.
> Usualy because the need of performance and additiona redundancy/fault 
> tollerance.
> So if u need performance a "Software RAID Solution" would always be a 
> bad choice.
Why?  Do you have any benchmarks that show that software raid is slower 
than hardware raid?

Anyway, still doesn't answer my question.

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Bryn M. Reeves]

On Thu, 2009-04-09 at 09:17 +0200, Axel Werner wrote:
> Why you need RAID 10 at all ?
> 
> Usualy because the need of performance and additional redundancy/fault 
> tollerance.
> So if u need performance a "Software RAID Solution" would always be a 
> bad choice. If you need some sort of redundancy and no performance, go 
> for it. if u need performance youll better get yourself a real HARDWARE 
> RAID CONTROLLER for your drives. Those cost a bit. but are worth it.

Common myth; as John says please present benchmarks to support this.
While there are some advantages to hardware RAID that can be a benefit
in some situations it's not safe to assume that the hardware solution
outperforms the software approach. It can do but usually only when the
number of disks to manage reaches a level where PCI bus saturation
becomes an issue. Below this point, particularly for RAID levels
involving parity calculations software will often outperform a hardware
solution (it uses the host CPU for these calculations instead of the
itty-bitty embedded processor on the RAID card).

> Best RAID Controllers around i do know are those from ICP VORTEX 
> (meanwhile belongs to Adaptec). Best Linux Support ever! Accustic alarm, 
> SNMP, GUI, CLI Interfaces and Text-oriented tools to handle/configure 
> the raid controller within the running os and all.

ICP Vortex use the aacraid chipset from Adaptec (also shipped in
different forms by a number of other OEMs and system integrators).

> also working good with linux are LSI Logic MEgaRaids. BUT... they dont 
> support GNU Linux , only RH Enterprise and Suse Enterprise are 

What are you talking about? The megaraid driver has been in the kernel
for years now. It's been a very long time since you had to use
out-of-tree modules for these cards (even if the vendors still provide
their own packaged binary modules).

> DO NOT USE CHEAP "PSEUDO HARDWARE RAID CONTROLLERS" like DAWI Controll, 
> Silicon Chip crap or those other 150$ shity RAID 0 or RAID 1 crap. those 
> cheap controllers are NO REAL HARDWARE RAIDs. Those are just simple 
> ATA/SATA Adapters with a "more advanced driver". Those Raid controllers 

The vendor provided drivers for these cards are generally junk. Most ATA
soft-RAID cards now work reasonably well with the dmraid tools.

> are NOTHING without their drivers. just a bunch of disks. And that is 
> what you usualy can see if you boot a linux on such a controller. even 
> if you have configured a RAID5 or RAID1 with only ONE logical drive, 

RAID5 with one drive?

> those controllers will still present ALL physical DRIVES to the OS as 
> there would be no RAID configuration at all. Drop those controllers... 
> trash em.

Yep, that's where dmraid comes in - it interprets the on-disk metadata
and generates an appropriate device-mapper table to map the arrays on
the disks without any need for the proprietary drivers.

Regards,
Bryn.

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Mark H. Wood]

[-- Attachment #1: Type: text/plain, Size: 1318 bytes --]

On Thu, Apr 09, 2009 at 12:45:13PM +0100, Bryn M. Reeves wrote:
> On Thu, 2009-04-09 at 09:17 +0200, Axel Werner wrote:
> > also working good with linux are LSI Logic MEgaRaids. BUT... they dont 
> > support GNU Linux , only RH Enterprise and Suse Enterprise are 
> 
> What are you talking about? The megaraid driver has been in the kernel
> for years now. It's been a very long time since you had to use
> out-of-tree modules for these cards (even if the vendors still provide
> their own packaged binary modules).

He probably is referring to the userland tools for managing the
controllers, which are useless on most distros.  Which makes the
hardware much less valuable, since you have to down the system and get
into the adaptor's BIOS just to look at it, let alone adjust it.  See
for example *any* HP storage or system-management product.  The tools
will not even load -- they depend on versions of libstdc++ that do not
and will never exist in most distros.

The megaraid (and cciss) drivers *have* been in-kernel for a long time
now and *do* work well -- once you get the adaptor set up from BIOS.
As long as you're happy to set-and-forget, they are good choices.

-- 
Mark H. Wood, Lead System Programmer   mwood@IUPUI.Edu
Friends don't let friends publish revisable-form documents.

[-- Attachment #2: Type: application/pgp-signature, Size: 198 bytes --]

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Stuart D. Gathman]

On Thu, 9 Apr 2009, John Hughes wrote:

> > So if u need performance a "Software RAID Solution" would always be a bad
> > choice.
> Why?  Do you have any benchmarks that show that software raid is slower than
> hardware raid?

For RAID 1 and 0, software RAID is as fast or faster in my experience.
If you think about it, the software is just coordinating DMA transfers,
no actual processing.  It is RAID 5 and similar configurations that benefit
from hardware implementation.  My experience has been with the 'md' driver
and AIX LVM, not with Linux LVM mirroring/striping, however.

A big drawback of controller based hardware RAID is the requirement
to have same sized drives (or waste the difference).  With software RAID (and
with high end sub-system based hardware RAID), you can mix a variety of drive
sizes.  I typically use RAID 1, and I like to expand storage by just 
adding a drive in the size du jour (500G today, 1T tomorrow), and doing
a few pvmoves to expand mirrored space.  (And you can also move md
mirrors while in operation with judicious use of mdadm -a and mdadm -f,
the tricky part being no changes to a partition table while a partition is
in use).

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Greg Bledsoe]

I have to take issue with that.  Software raid is almost always faster
than hardware raid on any modern system.  I've run into a few special
cases where this isn't true, usually involving a database,
replication, and very large onboard raid cache.

Not to mention that adding a raid card is a single point of failure
and *poof* --  hope you had current backups.


On 4/9/09, Axel Werner <mail@awerner.homeip.net> wrote:
> Why you need RAID 10 at all ?
>
> Usualy because the need of performance and additional redundancy/fault
> tollerance.
> So if u need performance a "Software RAID Solution" would always be a
> bad choice. If you need some sort of redundancy and no performance, go
> for it. if u need performance youll better get yourself a real HARDWARE
> RAID CONTROLLER for your drives. Those cost a bit. but are worth it.
>
> Best RAID Controllers around i do know are those from ICP VORTEX
> (meanwhile belongs to Adaptec). Best Linux Support ever! Accustic alarm,
> SNMP, GUI, CLI Interfaces and Text-oriented tools to handle/configure
> the raid controller within the running os and all.
>
> 2nd best are ADAPTEC Raid controllers,
>
> also working good with linux are LSI Logic MEgaRaids. BUT... they dont
> support GNU Linux , only RH Enterprise and Suse Enterprise are
> supported. All software comes within RPM packages. (pretty bullshit!) -
> The only thing that works good is a CLI tool. with some scripting you
> can monitor your drives and raid within the os then. no accustic alarm.
> pretty crappy.
>
> DO NOT USE CHEAP "PSEUDO HARDWARE RAID CONTROLLERS" like DAWI Controll,
> Silicon Chip crap or those other 150$ shity RAID 0 or RAID 1 crap. those
> cheap controllers are NO REAL HARDWARE RAIDs. Those are just simple
> ATA/SATA Adapters with a "more advanced driver". Those Raid controllers
> are NOTHING without their drivers. just a bunch of disks. And that is
> what you usualy can see if you boot a linux on such a controller. even
> if you have configured a RAID5 or RAID1 with only ONE logical drive,
> those controllers will still present ALL physical DRIVES to the OS as
> there would be no RAID configuration at all. Drop those controllers...
> trash em.
>
> Get ICP Vortex (Adaptec) and Adaptec - Those Rock!
>
> greets
> Axel
>
>
>
> Am 08.04.2009 15:11, John Hughes schrieb:
>>                if (lp->stripes > 1) {
>>                        log_error("mirrors and stripes are currently "
>>                                  "incompatible");
>>                        return 0;
>>                }
>>
>> Should I just stick with mdadm for my mirroring and striping needs?
>>
>> _______________________________________________
>> linux-lvm mailing list
>> linux-lvm@redhat.com
>> https://www.redhat.com/mailman/listinfo/linux-lvm
>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

-- 
Sent from my mobile device

Greg

Prosperity is only an instrument to be used, not a deity to be worshipped.
-- Calvin Coolidge

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Harald Milz]

Short version: Go read http://linuxmafia.com/faq/Hardware/sata.html, and don't
make softraid worse than it is. 

On Thu, Apr 09, 2009 at 09:17:33AM +0200, Axel Werner wrote:
> DO NOT USE CHEAP "PSEUDO HARDWARE RAID CONTROLLERS" like DAWI Controll, 

(lotsa yelling deleted)


-- 
Idiot Box, n.:
	The part of the envelope that tells a person where to place the
stamp when they can't quite figure it out for themselves.
		-- Rich Hall, "Sniglets"

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[John Hughes]

John Hughes wrote:
>                if (lp->stripes > 1) {
>                        log_error("mirrors and stripes are currently "
>                                  "incompatible");
>                        return 0;
>                }
>
> Should I just stick with mdadm for my mirroring and striping needs?
So, ignoring the hijacking of this thread by people proposing hardware 
solutions, the answer is "nobody who knows reads this list"?

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[malahal]

John Hughes [john@Calva.COM] wrote:
> John Hughes wrote:
>>                if (lp->stripes > 1) {
>>                        log_error("mirrors and stripes are currently "
>>                                  "incompatible");
>>                        return 0;
>>                }
>>
>> Should I just stick with mdadm for my mirroring and striping needs?

You can do it today with some hassle or wait until someone implements a
feature called 'generic layering'. The feature really means, treat some
LVs as PVs!

How can you do raid10 today? Create two raid0 LVs. Lets us call these
lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.

Isn't that a rai10 volume?

Thanks, Malahal.

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[John Hughes]

malahal@us.ibm.com wrote:
> John Hughes [john@Calva.COM] wrote:
>   
>> John Hughes wrote:
>>     
>>>                if (lp->stripes > 1) {
>>>                        log_error("mirrors and stripes are currently "
>>>                                  "incompatible");
>>>                        return 0;
>>>                }
>>>
>>> Should I just stick with mdadm for my mirroring and striping needs?
>>>       
>
> You can do it today with some hassle or wait until someone implements a
> feature called 'generic layering'. The feature really means, treat some
> LVs as PVs!
>
> How can you do raid10 today? Create two raid0 LVs. Lets us call these
> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.
>
> Isn't that a rai10 volume?
>   
To increase the chances of surviving a double-disk failure it would be 
better to raid-0 a bunch of raid-1's.

Are we sure there are no deadlock problems with LVM2 layered on top of LVM2?

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[Drew]

In my experience, on the linux platform it's easier to avoid LVM's
raid-like features and let software raid, specifically md, handle the
raid for you. It's another layer to manage but not much more
complexity.

Not to knock on the LVM folks, they do awesome work, but imho the code
for the software raid is better tested if only by virtue of how often
it's used/tested/broken. LVM, as I see it, is designed to take
physical disks/arrays and hide the underlying structure into one giant
pool for the admin to manage.


-- 
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[Mark Krenz]

On Mon, Apr 13, 2009 at 02:30:27PM GMT, Sandeep K Sinha [sandeepksinha@gmail.com] said the following:
> >
> >> To increase the chances of surviving a double-disk failure it would be
> >> better to raid-0 a bunch of raid-1's.
> >
> > This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to
> > 0+1 not only because of the improved redundancy but also the individual
> 
> I disagree.
> 
> Look at this:
> http://www.pcguide.com/ref/hdd/perf/raid/levels/multXY-c.html

  I misread what Bryn had said at first as well, but re-reading it, he
means that RAID1+0 does better at recovery than RAID0+1, which does make
sense.  In RAID0+1, depending on how many mirror arrays you have and how
smart your RAID controller is, you could have twice as many disk
accesses happening during a disk recovery.  The URL that you pointed too
doesn't really talk about performance during a recovery anyways.


-- 
Mark S. Krenz
IT Director
Suso Technology Services, Inc.
http://suso.org/

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[Bryn M. Reeves]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

John Hughes wrote:
> malahal@us.ibm.com wrote:
>> John Hughes [john@Calva.COM] wrote:
>>  
>>> John Hughes wrote:
>>>    
>>>>                if (lp->stripes > 1) {
>>>>                        log_error("mirrors and stripes are currently "
>>>>                                  "incompatible");
>>>>                        return 0;
>>>>                }
>>>>
>>>> Should I just stick with mdadm for my mirroring and striping needs?
>>>>       
>>
>> You can do it today with some hassle or wait until someone implements a
>> feature called 'generic layering'. The feature really means, treat some
>> LVs as PVs!
>>
>> How can you do raid10 today? Create two raid0 LVs. Lets us call these
>> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
>> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.
>>
>> Isn't that a rai10 volume?

No, it's a RAID 0+1 (RAID01/mirror of stripes).

> To increase the chances of surviving a double-disk failure it would be
> better to raid-0 a bunch of raid-1's.

This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to
0+1 not only because of the improved redundancy but also the individual
mirror sets can have failures and recover independently. When a strip
set in a RAID0+1 fails the entire mirror must be re-synchronised giving
longer recovery times and more performance degradation during the rebuild.

> Are we sure there are no deadlock problems with LVM2 layered on top of
> LVM2?

Stacked volumes work fine, there's just limited support in the tools for
creating them without going to a lot of manual effort at the moment.

Regards,
Bryn.
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Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[Sandeep K Sinha]

On Mon, Apr 13, 2009 at 5:55 PM, Bryn M. Reeves <bmr@redhat.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> John Hughes wrote:
>> malahal@us.ibm.com wrote:
>>> John Hughes [john@Calva.COM] wrote:
>>>
>>>> John Hughes wrote:
>>>>
>>>>> � � � � � � � �if (lp->stripes > 1) {
>>>>> � � � � � � � � � � � �log_error("mirrors and stripes are currently "
>>>>> � � � � � � � � � � � � � � � � �"incompatible");
>>>>> � � � � � � � � � � � �return 0;
>>>>> � � � � � � � �}
>>>>>
>>>>> Should I just stick with mdadm for my mirroring and striping needs?
>>>>>
>>>
>>> You can do it today with some hassle or wait until someone implements a
>>> feature called 'generic layering'. The feature really means, treat some
>>> LVs as PVs!
>>>
>>> How can you do raid10 today? Create two raid0 LVs. Lets us call these
>>> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
>>> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.
>>>
>>> Isn't that a rai10 volume?
>
> No, it's a RAID 0+1 (RAID01/mirror of stripes).
>
>> To increase the chances of surviving a double-disk failure it would be
>> better to raid-0 a bunch of raid-1's.
>
> This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to
> 0+1 not only because of the improved redundancy but also the individual

I disagree.

Look at this:
http://www.pcguide.com/ref/hdd/perf/raid/levels/multXY-c.html

> mirror sets can have failures and recover independently. When a strip
> set in a RAID0+1 fails the entire mirror must be re-synchronised giving
> longer recovery times and more performance degradation during the rebuild.
>



>> Are we sure there are no deadlock problems with LVM2 layered on top of
>> LVM2?
>
> Stacked volumes work fine, there's just limited support in the tools for
> creating them without going to a lot of manual effort at the moment.
>
> Regards,
> Bryn.
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.4.9 (GNU/Linux)
> Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org
>
> iEYEARECAAYFAknjL1cACgkQ6YSQoMYUY96uPACeNwylwf1aeZuAzYxHWGJhH7Je
> LHMAnjLy4NB77gUiABVUkiKeCAMpbGU4
> =lv0v
> -----END PGP SIGNATURE-----
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>



-- 
Regards,
Sandeep.





 	
�To learn is to change. Education is a process that changes the learner.�

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

[Luca Berra]

On Thu, Apr 09, 2009 at 09:17:33AM +0200, Axel Werner wrote:
> Why you need RAID 10 at all ?
>
> Usualy because the need of performance and additional redundancy/fault 
> tollerance.
> So if u need performance a "Software RAID Solution" would always be a bad 
> choice. If you need some sort of redundancy and no performance, go for it. 
> if u need performance youll better get yourself a real HARDWARE RAID 
> CONTROLLER for your drives. Those cost a bit. but are worth it.

i have a couple usage cases for raid10 that make your point ridiculus

i have two san attached storages in two different buildings,
they present a number of lun (each is raid-5 (3+1)). those will likely
outperform your icp vortex by some order of magnitude, still it is not
enough for me, so i would use striping, between different luns to
achieve more iops.

now i said they were 2 and in two different buildings, this is why i use
mirroring, in case an entire building is unavailable. yes i have servers
in both building.

having this integrated seamlessly in lvm would be nice, so i could use
lvm locking integration with cluster software.

the other scenario is when i already have a striped lv and want to
mirror it for migration to a different storage.

L.

-- 
Luca Berra -- bluca@comedia.it
          Communication Media & Services S.r.l.
   /"\
   \ /     ASCII RIBBON CAMPAIGN
    X        AGAINST HTML MAIL
   / \

Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?

[Bryn M. Reeves]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Sandeep K Sinha wrote:
> On Mon, Apr 13, 2009 at 5:55 PM, Bryn M. Reeves <bmr@redhat.com> wrote:
> John Hughes wrote:
>>>> malahal@us.ibm.com wrote:
>>>>> John Hughes [john@Calva.COM] wrote:
>>>>>
>>>>>> John Hughes wrote:
>>>>>>
>>>>>>>                if (lp->stripes > 1) {
>>>>>>>                        log_error("mirrors and stripes are currently "
>>>>>>>                                  "incompatible");
>>>>>>>                        return 0;
>>>>>>>                }
>>>>>>>
>>>>>>> Should I just stick with mdadm for my mirroring and striping needs?
>>>>>>>
>>>>> You can do it today with some hassle or wait until someone implements a
>>>>> feature called 'generic layering'. The feature really means, treat some
>>>>> LVs as PVs!
>>>>>
>>>>> How can you do raid10 today? Create two raid0 LVs. Lets us call these
>>>>> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
>>>>> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.
>>>>>
>>>>> Isn't that a rai10 volume?
> No, it's a RAID 0+1 (RAID01/mirror of stripes).
> 
>>>> To increase the chances of surviving a double-disk failure it would be
>>>> better to raid-0 a bunch of raid-1's.
> This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to
> 0+1 not only because of the improved redundancy but also the individual
> 
>> I disagree.
> 
>> Look at this:
>> http://www.pcguide.com/ref/hdd/perf/raid/levels/multXY-c.html

What do you disagree with?

The article you linked to points out the same robustness and recovery
concerns with a 0+1 layout as I mentioned earlier. It then goes on to
say that this could be mitigated for 0+1 by a smart RAID implementation
that continues to stripe to partially-failed RAID 0 sets but that most
actual RAID controllers don't chose to implement this.

The article seems to make the same claims as I did.

Regards,
Bryn.

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Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org

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