[DRBD-user] SAN, drbd, ha, shared disks, ataoe, iscsi, gnbd

Maciej Bogucki macbogucki at gmail.com
Tue Aug 12 16:30:42 CEST 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Alex wrote:
> On Tuesday 12 August 2008 12:52, you wrote:
>   
>> Alex wrote:
>>     
>>> Hello experts,
>>>
>>> I read that raid software on linux is not cluster aware, so i'm trying to
>>> find a solution to join together more computers to form a shared file
>>> system and build a SAN (correctly if i am wrong), avoiding usage of raid
>>> software.
>>>
>>> Let say that I have:
>>> - N computers (N>8) sharing their volumes (volX, where X=N). Each volX is
>>> arround 120GB.
>>> - M servers (M>3) - which are accessing a GFS volume (read/write)
>>> - Other regular computers which are available if required.
>>>
>>> Now, I want:
>>> - to build somehow a GFS on top of vol1, vol2, ... volN volumes with high
>>> data availability and without a single point of failure.
>>>       
>> If You want to use GFS, You would need one volX exported via iSCSI or
>> GNDB to M servers. 
>>     
>
> This exactly what i have now on one of M servers:
> [root at rhclm ~]# lsscsi
> [0:0:0:0]    disk    IET      VIRTUAL-DISK     0     /dev/sda
> [1:0:0:0]    disk    IET      VIRTUAL-DISK     0     /dev/sdb
> [root at rhclm ~]#
>
> here, sda and sdb are block devices imported via iscsi from computer1 and 
> computer2.
>
> Question: is possible to group sda and sdb using raid1 software in an array 
> (/dev/md0) and after that, on top of md0 to create a logical volume and run 
> GFS?
>
> AFAIK THIS DESIGN IS IMPOSSIBLE because raid software on linux is NOT 
> CLUTER-AWARE? So, just using iscsi (or gnbd) to export volX is NOT ENOUGH 
> because if i am loosing one computerX i am loosing all data on GFS! Right?
>
>   
here is the answer 
http://www.redhat.com/magazine/009jul05/departments/tips_tricks/
>> For HA you could use DRBD - two volumes vol1, vol2 
>> created as /dev/drbd0 and exported to M servers.
>>     
>
> yes, thats why i want to use drbd, to replace raid1 limitations and group 
> computerX two by two. In this scenario, remain just one question: how can i 
> join together /dev/drbd*, or....if this thing is not possible, the question 
> is: how can i join together all 8 volX in order to have:
> - Fault-tolerance: Failure of a single drive (volX) or server (computerX) 
> should not bring down the GFS!
>   
This isn't the limit of GFS. You can't use DRBD with iSCSI or GNBD 
because  DRBD support only two nodes and You have eight.
GFS need shared storage(SAN) - one raw device which could be visible on 
the few nodes.
>   
>> Your solution isn't good for GFS fs.
>>     
>
> i am looking to find it, that's why i'm here...  can you suggest me one?
>
>   
I can't help You because I did tested any of them ;(
>> You can also use other HA/Cluster fs like: hadoop, gluster, kosmos-fs,
>> mogile and much more.
>>     
>
> I read about lustre (from SUN Microsistems). It seems that is well supported 
> on linux (centos5/rhel5) and has support for raid/lvm/iscsi, is scaling well 
> and is easy to extend. Is that correct? Using lustre can i join all volX 
> (exported via iscsi) toghether in one bigger volume (using raid/lvm) and have 
> a SHARED STORAGE?
>   
I think You are right.

Best Regards
Maciej Bogucki



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