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Laurent Blume | 1 Mar 20:55
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Best use of ZFS on 4 disks

Hi all,

I'm going to get myself 4 disks, to make a pool that can sustain the 
loss of 2 of them.

What would be the best way with ZFS? RAIDZ2? 2 mirrors in the same pool?

Laurent

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Ian Collins | 1 Mar 21:07
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Re: Best use of ZFS on 4 disks

Laurent Blume wrote:

>Hi all,
>
>I'm going to get myself 4 disks, to make a pool that can sustain the 
>loss of 2 of them.
>
>What would be the best way with ZFS? RAIDZ2? 2 mirrors in the same pool?
>
>  
>
I'm doing the same, with a mirror of two stripes.  This should give the
best performance and redundancy.

Ian

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Chad Leigh -- Shire.Net LLC | 1 Mar 21:24

Re: Best use of ZFS on 4 disks


On Mar 1, 2007, at 1:07 PM, Ian Collins wrote:

> Laurent Blume wrote:
>
>> Hi all,
>>
>> I'm going to get myself 4 disks, to make a pool that can sustain the
>> loss of 2 of them.
>>
>> What would be the best way with ZFS? RAIDZ2? 2 mirrors in the same  
>> pool?
>>
>>
>>
> I'm doing the same, with a mirror of two stripes.  This should give  
> the
> best performance and redundancy.

I am not sure how ZFS does this but will that really sustain the  
simultaneous loss of 2 disks?  Say I lose one out of each stripe set.

Again, I am not a storage guru, but in laymen thinking about it this  
would worry me in this setup.  raidz2 would seem the better choice?

Chad

---
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Laurent Blume | 1 Mar 21:31
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Re: Best use of ZFS on 4 disks

Chad Leigh -- Shire.Net LLC a écrit :
> I am not sure how ZFS does this but will that really sustain the  
> simultaneous loss of 2 disks?  Say I lose one out of each stripe set.
> 
> Again, I am not a storage guru, but in laymen thinking about it this  
> would worry me in this setup.  raidz2 would seem the better choice?

Yes, I'm thinking along the same lines. You can lose 2 disks in a 
striped mirror, but not *any* disks. But performance should be much 
better too.

BTW, Ian, how do you do that? The man gives an example to put 2 mirror 
vdevs in a single pool, but this is not striped, right?
Or were you talking about that old-fashioned UFS thing? :-)

Laurent

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Dick Hoogendijk | 1 Mar 21:38
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webmail on solaris10


I used squirrelmail on my solaris10 with cyrus imap server and
sendmail. This worked perfectly fine 'till today. I upgraded to
PHP-5.2.1 and now there are calls to non existing functions like
session_start() and session_id()

Does anybody have a recommendation for a good working webmail package.
NO maildirs (cyrus). I have users depending on this service. Blastwave
has "no return" to php-5.2 .. What to do?

--

-- 
Dick Hoogendijk -- PGP/GnuPG key: F86289CE
++ http://nagual.nl/ | Solaris 10 11/06 ++

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Ian Collins | 1 Mar 21:47
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Re: Best use of ZFS on 4 disks

Chad Leigh -- Shire.Net LLC wrote:

>On Mar 1, 2007, at 1:07 PM, Ian Collins wrote:
>  
>
>>Laurent Blume wrote:
>>    
>>
>>>Hi all,
>>>
>>>I'm going to get myself 4 disks, to make a pool that can sustain the
>>>loss of 2 of them.
>>>
>>>What would be the best way with ZFS? RAIDZ2? 2 mirrors in the same  
>>>pool?
>>>      
>>>
>>I'm doing the same, with a mirror of two stripes.  This should give  
>>the
>>best performance and redundancy.
>>    
>>
>
>I am not sure how ZFS does this but will that really sustain the  
>simultaneous loss of 2 disks?  Say I lose one out of each stripe set.
>
>  
>
No, that's equivalent to loosing both drives in a mirror.
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Ian Collins | 1 Mar 21:49
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Re: Best use of ZFS on 4 disks

Laurent Blume wrote:

>Chad Leigh -- Shire.Net LLC a écrit :
>  
>
>>I am not sure how ZFS does this but will that really sustain the  
>>simultaneous loss of 2 disks?  Say I lose one out of each stripe set.
>>
>>Again, I am not a storage guru, but in laymen thinking about it this  
>>would worry me in this setup.  raidz2 would seem the better choice?
>>    
>>
>
>BTW, Ian, how do you do that? The man gives an example to put 2 mirror 
>vdevs in a single pool, but this is not striped, right?
>Or were you talking about that old-fashioned UFS thing? :-)
>
>  
>
Stripe two pairs of drives and mirror the stripes.

Ian

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Laurent Blume | 1 Mar 22:27
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Re: Best use of ZFS on 4 disks

Ian Collins wrote:
> Stripe two pairs of drives and mirror the stripes.

You mean, using SVM for the stripes?

I've found the 4 disk config is an example in the doc:

For example, you could create the following configurations out of 4 disks:
    * Four disks using dynamic striping
    * One four-way RAID-Z configuration
    * Two two-way mirrors using dynamic striping

http://docs.sun.com/app/docs/doc/819-5461/6n7ht6qrr?a=view

But I'm still lost about striping, If not SVM, what's the zpool command
to use it? Sorry for being slow to understand!

Laurent

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Ian Collins | 1 Mar 23:14
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Re: Best use of ZFS on 4 disks

Laurent Blume wrote:

>Ian Collins wrote:
>  
>
>>Stripe two pairs of drives and mirror the stripes.
>>    
>>
>
>You mean, using SVM for the stripes?
>
>  
>
Sorry, posting pre-coffee!

>I've found the 4 disk config is an example in the doc:
>
>For example, you could create the following configurations out of 4 disks:
>    * Four disks using dynamic striping
>    * One four-way RAID-Z configuration
>    * Two two-way mirrors using dynamic striping
>
>http://docs.sun.com/app/docs/doc/819-5461/6n7ht6qrr?a=view
>
>But I'm still lost about striping, If not SVM, what's the zpool command
>to use it? Sorry for being slow to understand!
>
>  
>
I'm not 100% sure it's the optimum way (still waiting for the parts!),
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Laurent Blume | 1 Mar 23:33
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Re: Best use of ZFS on 4 disks

Ian Collins a écrit :
> Sorry, posting pre-coffee!

And after a long work day and 2 hours at the gym for me, so we're both 
excused ;-)

> I'm not 100% sure it's the optimum way (still waiting for the parts!),
> but I think the example (
> 
> *zpool create tank mirror c1d0 c2d0 mirror c3d0 c4d0) is the way to do this.

Ok, that's the manual example. I thought it was only a concat, but on 
second thought, you're certainly right, ZFS must be intelligent enough 
to stripe over the mirrors, since the spool spans over both.

The docs should explain it a bit more explicitly, it's such a change 
from other systems, but it's sure great. I'm barely starting to really 
use it, and I'm very, very impressed.

Laurent

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