Internal metadata, and why we recommend it

August 20, 2009

One of the things that repeatedly seem to puzzle users about the DRBD is the question of whether to use internal or external metadata. Remember, DRBD sets aside a small area on a local disk (on every cluster node) where it keeps the Activity Log, the quick-sync bitmap, data generation UUIDs, and a few other bits and pieces for local housekeeping.

The specific aspect that is to be discussed here is the Activity Log. Without going into too much detail, let’s be satisfied with the factoid that DRBD “occasionally” (it’s a little more involved in reality) writes to the AL, and has to wait for that write to complete before it can handle user data again. This wait is the crucial point. It’s usually on the order of just a few milliseconds, but on busy systems this can add up to where it throttles throughput just a little.

Now, what makes I/O fast or slow (on rotational hard drives, solid state is a different matter)? That’s right, it’s disk seeks. So when we use internal meta data, so the theory goes, the read-write head has to do something in the data area, then move to the AL and do something there, then move back to the data area, and so forth. Which, intuitively, can be speeded up if you put user data and meta data on different spindles. Different “logical” disks won’t do, it has to be on a separate spindle, so read-write heads can move in parallel. Again, this is as the naïve theory goes. Use external meta data, devise a clever scheme on how to spread your meta data apart from your user data, and you’ll be fine. And you can call yourself a great wizard in storage subsystem tuning. Well, not quite, unfortunately.

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Liveblog: LINBIT at Chemnitzer Linuxtage 2009

March 14, 2009

Today (Saturday 3/14) and tomorrow (Sunday 3/15) Martin Loschwitz and myself are presenting open source high availability at Chemnitzer Linuxtage in Chemnitz, Germany. As I am blogging this, Martin is speaking to a packed auditorium of about 200-or-so attendees (I’m terrible at estimating crowds). Read the rest of this entry »

MySQL on DRBD, again and again

March 13, 2009

MySQL Conference & Expo 2009For those of you interested in high availability for databases, this week brought a whole flurry of DRBD related posts in the MySQL blogosphere. Read the rest of this entry »

MySQL Live Webinar, Feb 11, 1800 UTC

February 9, 2009

This week, Sun hosts a live webinar on accelerating MySQL and DRBD in scale-out environments, in which yours truly will be covering the DRBD part. Besides DRBD for Dolphin Express, the webinar will also cover how to use Dolphin Express to accelerate MySQL Cluster and MySQL Replication.

Registration for this webinar is now open. See you on Wednesday!

A few seats still left for DRBD Performance Tuning webinar

August 19, 2008

For those of you interested in getting maximum performance out of your DRBD-based HA clusters, I am hosting a webinar on the subject on Wednesday, 8/27 at 1800 UTC (2pm Eastern, 11am Pacific).

The webinar is offered free of charge and it’s already pretty tight in terms of attendance, the event being limited to a maximum of 60 attendees. But if you’re quick, you might still stand a chance of grabbing a front-row seat. Check out this page on our website, it has all the relevant information.