Kevin Closson's Blog: Platforms, Databases and Storage

In this press release, Oracle has started making the existence of the Oracle Linux Test Kit a bit more widely known. I’ve been playing with this kit for a little while now and planned to blog my experiences. It has test components that work against Oracle instances. I’ll blog about my findings as soon as I can.

Long Live AdvFS?
The press release also announces Oracle’s new open source file system called Btrfs. If it was just another file system I wouldn’t mention it in my blog, but the project page mentions plans for features that I think are absolutely critical such as:

1. Space efficient packing of small files
2. Writable snapshots
3. Object level mirroring and striping
4. Strong integration with device mapper for multiple device support
5. Efficient incremental backup and FS mirroring

This thing sure smells like a reincarnation of AdvFS, but what do I know?

The project page states that the developers are not even looking into database workloads at the moment but since it is an extent based filesystem I see no reason it wouldn’t work quite well with Oracle databases. I’m most keen on the list of features I’ve listed above though because they go a long way to make life better in production Oracle environments. First, number 1 on the list is good handling of small files. This will be a boon for the handling of trace and logging and a lot of the other ancillary file creation that goes on external to the database. Small files (at least myriads of them) are the bane of most filesystems.

Next on the list are clones-or as the project page calls them writable snapshots. Veritas has offered these for quite some time and they are a very nice feature for creating working copies of databases that are current up to the moment you create the snapshot. Creating a snapshot doesn’t impact performance and a good implementation of clones will not impact the real database even if you are doing a reasonable amount of writes on the clone. Also very cool!

Then there is number 3 on the list-object level mirroring and striping. When all good filesystems “grow up” they offer this sort of feature. Being able to implement software RAID on a file basis is the ultimate cool and I can’t wait to give this one a play! Being able to hand pick which Oracle files-or general purpose files-upon which to apply varying software RAID characteristics is a very nice feature.

Number 4 on the list is Device Mapper support. I’ve ranted on my blog and other forums about Linux handling of device names for quite some time and DM goes a long way to address the pet-peaves. Seeing this filesystem exploit DM at design level is a good thing.

Finally, number 5 above suggests good support for filesystem mirroring. This technology has proven itself useful for Veritas and NetApp customers-as well as others. It’s good to see it in Btrfs.

Clustered Btrfs?
Some time back I made a blog entry about ZFS and discussed the notion of “cluster butter.” That notion refers the the idea that you can take any filesystem and “clusterize” it. Generally adding cluster support after the design phase does not produce much of a cluster filesystem. So, I intend to dive in to see what underpinnings there are in Btrfs for future cluster support.