Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
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 > (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 DRBD. 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 -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 198 bytes Desc: This is a digitally signed message part URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20100203/cf6d668a/attachment.pgp>