Qwerty-1 umakantgoyal1 at gmail.com
Wed Feb 3 11:09:30 CET 2010

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

Hi Mark,

Thanks. sorry for weired questions. Problem is that i am not able to make
picture in mind how all the stuff is working.i know how DRBD works. but i am
not able to relate DRBD with RAID.
Can we use DRBD without RAID? 


Mark Watts wrote:
> On Tue, 2010-02-02 at 20:51 -0800, Qwerty-1 wrote:
>> Hi Mark,
>> Thanks, what i understood that, to replicate the data locally we need
>> (RAID helps to decide which data need to be replicated).
> Not quite.
> Hardware RAID (for example) as performed by a dedicated controller, will
> take disks and use them in their entirety. The Operating System will see
> *one* disk per Logical Disk you create.
> Software RAID can work at either disk level or partition level (where
> not all of the disk is used). The Operating System will see all of the
> component disks, along with a "RAID device" which you actually format,
> mount and store data on.
> In both cases the replication is automatic and total. You don't get to
> choose whether data is processed or not.
> RAID is mostly used by folks who want to mitigate the risk of a disk
> failure. Some RAID levels use more than one disk and as a side-effect
> they may provide more performance.
>> But if we want to
>> replicate the date over network then we need DRBD with RAID. In later
>> case,
>> DRBD will help to transfer data over network (other machine) by making
>> TCP
>> connectiong and RAID will help to decide which data needs to be
>> replicated.
>> Please correct me if i am wrong.
> DRBD is another layer in the storage stack, responsible for ensuring
> that any data written to a DRBD block device is replicated to a remote
> node, thus allowing for certain types of high-availability and/or
> fail-over.
> For example, you might have the following (ignoring boot partitions):
> /dev/sda        # disk #1
> /dev/sdb        # disk #2 
>   /dev/md0      # Linux software raid-1 mirror
>     /dev/drbd0  # DRBD Replicated filesystem
> You would then create your filesystem (ext3 or whatever)
> using /dev/drbd0.
> Assuming you've setup another node in a similar way, and DRBD is working
> correctly, any data you write to /dev/drbd0 will be both replicated to
> the remote node, and also mirrored on the local disks.
> In this situation, RAID will be protecting you against disk failure, and
> DRBD will be protecting you against machine failure.
> http://www.drbd.org/users-guide/ is the best place to learn more about
> Regards,
> Mark.
> -- 
> Mark Watts BSc RHCE MBCS
> Senior Systems Engineer, Managed Services Manpower
> www.QinetiQ.com
> QinetiQ - Delivering customer-focused solutions
> GPG Key: http://www.linux-corner.info/mwatts.gpg
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