Mirrored SAN vs. DRBD

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Every now and then we get asked “why not simply use a mirrored SAN instead of DRBD®”? This post shows some important differences.

Basically, the first setup is having two servers, one of them being actively driving a DM-mirror (RAID1) over (eg.) two iSCSI volumes that are exported by two SANs; the alternative is using a standard DRBD setup. Please note that both setups need some kind of cluster manager (like Pacemaker).

Here are the two setups visualized:
The main differences are:

# SAN DRBD
1. High cost, single supplier Lower cost, commercial-off-the-shelf parts
2. At least 4 boxes (2 application servers, 2 SANs) 2 servers are sufficient
3. DM-Mirror has only recently got a write-intent-bitmap, and at least had performance problems (needed if active node crashes) Optimized Activity Log
4. Maintenance needs multiple commands Single userspace command: drbdadm
5. Split-Brain not automatically handled Automatical Split-Brain detection, policies via DRBD configuration
6. Data Verification needs to get all data over the network – twice Online-Verify transports (optionally) only checksums over the wire
7. Asynchronous mode (via WAN) not in standard product Protocol A available, optional proxy for compression and buffering
8. Black Box GPL solution, integrated in standard Linux Kernel since 2.6.33

So the Open-Source solution via DRBD has some clear technical advantages — not just the price.

And, if that’s not enough — with LINBIT® you get world-class support, too!

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Yusuf Yıldız

Yusuf Yıldız

After nearly 15 years of system and storage management, Yusuf started to work as a solution architect at Linbit. Yusuf's main focus is on customer success and contributing to product development and testing. As part of the solution architects team, he is one of the backbone and supporter of the sales team.

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Talk to us

LINBIT is committed to protecting and respecting your privacy, and we’ll only use your personal information to administer your account and to provide the products and services you requested from us. From time to time, we would like to contact you about our products and services, as well as other content that may be of interest to you. If you consent to us contacting you for this purpose, please tick above to say how you would like us to contact you.

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