[dm-devel] dm_mirror/dm_raid1 limitations ?.

[Suresh Babu Kandukuru]

What is difference of  creating mirror with 

1 ) mdadm (    mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1 --spare-devices=1 /dev/sdd1 ) 
and 
2)  dmsetup ( dmsetp create mirror )

Which one is better ?. and Pros and cons ?. Google is not helping much 
 
/Suresh


-----Original Message-----
From: Marian Csontos [mailto:mcsontos at redhat.com] 
Sent: Tuesday, January 27, 2015 12:32 AM
To: dm-devel at redhat.com
Subject: Re: [dm-devel] dm_mirror/dm_raid1 limitations ?.

On 01/26/2015 04:34 PM,  HYPERLINK "mailto:suresh.babu.kandukuru at oracle.com" suresh.babu.kandukuru at oracle.com wrote:
> Heinzm,thanks for the quick reply.. We are using dmestup create mirror 
> ..as we want to do that on physical San lun (block devices) ... Not 
> the one ( lv create ) you mentioned below.. Is there any advantage 
> going with logical volume approach lvcreate -type

One of LVM features is monitoring of mirror/raid LVs and removing/replacing any missing legs.

Using dmsetup directly, you have to do this manually.

>
> /Suresh
>
> Sent from my iPhone
>
>> On Jan 26, 2015, at 7:46 PM, Heinz Mauelshagen < HYPERLINK "mailto:heinzm at redhat.com" heinzm at redhat.com>
>> wrote:
>>
>>
>>> On 01/26/2015 02:51 PM, Suresh Babu Kandukuru wrote: Use case is
>>> : Two luns are mapped from storage array to linux host which are in 
>>> same SAN fabric . we want to create a mirror on the linux host with 
>>> these two luns and let  host use that mirror lun .  basic tests 
>>> suggest that dm_mirror working fine . when we have any intermittent 
>>> path issues with between host and san array , host i/o just freeze , 
>>> never returns back even after the path is online.
>>
>> Hard to tell what's happening without any kernel log.
>>
>>>
>>> Is dm_mirror viable solution here  ?. Can you point me any link 
>>> which gives the limitations of dm_mirror ? . another alternate 
>>> solutions you propose here ?. Thanks in advance .
>>
>> We've switched the default away from "mirror" to "raid1" in order to 
>> take advantage of th MD runtime. Have you tested  "lvcreate --type 
>> raid1 ..." yet? Please do.
>>
>> Regards, Heinz
>>
>>>
>>> Thanks /Suresh
>>>
>>>
>>> -- dm-devel mailing list  HYPERLINK "mailto:dm-devel at redhat.com" dm-devel at redhat.com 
>>> https://www.redhat.com/mailman/listinfo/dm-devel
>>
>> <Untitled.txt>
>
>
>
> -- dm-devel mailing list  HYPERLINK "mailto:dm-devel at redhat.com" dm-devel at redhat.com 
> https://www.redhat.com/mailman/listinfo/dm-devel
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