dm_mirror/dm_raid1 limitations ?.

dm_mirror/dm_raid1 limitations ?.

[Suresh Babu Kandukuru]

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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.  

 

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 .

 

Thanks

/Suresh

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Re: dm_mirror/dm_raid1 limitations ?.

[Heinz Mauelshagen]

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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
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel


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Re: dm_mirror/dm_raid1 limitations ?.

[suresh.babu.kandukuru]

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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  

/Suresh

Sent from my iPhone

> On Jan 26, 2015, at 7:46 PM, Heinz Mauelshagen <heinzm@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
>> dm-devel@redhat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
> 
> <Untitled.txt>

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Re: dm_mirror/dm_raid1 limitations ?.

[Marian Csontos]

On 01/26/2015 04:34 PM, suresh.babu.kandukuru@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 <heinzm@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 dm-devel@redhat.com
>>> https://www.redhat.com/mailman/listinfo/dm-devel
>>
>> <Untitled.txt>
>
>
>
> -- dm-devel mailing list dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>

Re: dm_mirror/dm_raid1 limitations ?.

[Suresh Babu Kandukuru]

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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@redhat.com] 
Sent: Tuesday, January 27, 2015 12:32 AM
To: dm-devel@redhat.com
Subject: Re: [dm-devel] dm_mirror/dm_raid1 limitations ?.

On 01/26/2015 04:34 PM,  HYPERLINK "mailto:suresh.babu.kandukuru@oracle.com" suresh.babu.kandukuru@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@redhat.com" heinzm@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@redhat.com" dm-devel@redhat.com 
>>> https://www.redhat.com/mailman/listinfo/dm-devel
>>
>> <Untitled.txt>
>
>
>
> -- dm-devel mailing list  HYPERLINK "mailto:dm-devel@redhat.com" dm-devel@redhat.com 
> https://www.redhat.com/mailman/listinfo/dm-devel
>

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