Thursday, July 03, 2008


Very interesting article written by Adam Leventhal.

I actually like the idea of L2ARC especially on low-end systems. Imagine a 1U or 2U x86 box with one internal disk being a 143GB SSD used for L2ARC - basically you getting 144GB fast read cache for your MySQL database (or anything else). You probably can't even put that much memory in 1U or 2U system in a first place (not to mention cost).

Now imagine much larger database. You buy additional entry-level array like Sun's 2540 and you put 12x143GB SSD drives for L2ARC (and at least one for SLOG if required). This gives you about 1,5TB of cache! You can cache relatively large database here.

Now I like the way L2ARC works - if you unmount ZFS pool and mount it again old L2ARC content will be re-used (thanks to ZFS checksums possible stale data will be detected, skipped and read from disks). What it means is that if you connect your 2540 (or whatever) full of SSD drives to a cluster and you failover your database along with your ZFS pool to another node your 1,5TB of cache will be still warm. So the impact of failover on your database performance can be greatly reduced.

Of course there are other scenarios and I'm keen to do some testing... :)

Wednesday, July 02, 2008

SystemTap (lack of) progress

I've just read a discussion on SystemTap. In a way it is a very sad read - couple of years later and SystemTap is nothing more than a toy for some kernel developers while DTrace has been in stable form for years now and is being widely used by kernel developers, application developers, system administrators, database administrators, etc. There is also a growing eco-system around DTrace - not only it has been ported to other OS'es but also there is a support for DTrace in Perl, Ruby, PHP, Postgress, MySQL, Xorg, ...

The key point about DTrace is that it just works and does its job.

It's been in use for so long now that it is no longer that exciting to use it - it is rather utterly frustrating when there is no DTrace around...

Bryan posted interesting comment about SystemTap.

Tuesday, July 01, 2008

NetApp vs. ZFS

Here is an update on the law-suit. If you are interested please also read a declaration by Dave Hitz. He basically does confess that NetApp is scared of ZFS and that it makes NetApp out of business. I agree - while I like NetApp from the economic point of view in most cases it doesn't make sense to buy it - build your storage box yourself using ZFS. Ok, you need certain skills to do so... but I'm 100% confident that sooner or later we will see appliances based on ZFS.

It's really sad that instead of innovating NetApp is going to court...