Native Linux ZFS kernel module and stability.

UPDATE: If you are interested in ZFS on linux you have two options at this point:

I have been actively following the  zfsonlinux project because once stable and ready it should offer surperior performance due to the extra overhead that would be incurred by using fuse with the zfs-fuse project.

You can see another one of my posts concerning zfsonlinux here.


There was a question posted in response to my previous blog post found here, about the stability of the native Linux ZFS kernel module release. I thought I would just make a post out of my response:

So far I have been able to perform some limited testing (given that the GA code was just released earlier this week), some time ago I had been given access to the beta builds,  so I had done some initial testing using those, I configured two mirrored vdevs consisting of two drives each. It seemed relatively stable as far as I was concerned, as I stated in my previous post…there is a known issue with the ‘zfs rollback’ command…which I tested using the GA release,  and I did in fact have problems with.

The work around at this point seems to be to perform a reboot after the rollback and then a ‘zfs scrub’ on the pool after the reboot. Personally I am hoping this gets fixed soon, because not everyone has the same level of flexibility, when it comes to rebooting their servers and storage nodes.

As far as I understand it, this module really consists of three pieces:

1)SPL -  a Linux kernel module which provides many of the Solaris kernel APIs. This layer makes it possible to run Solaris kernel code in the Linux kernel with relatively minimal modification.
2)ZFS – a Linux kernel module which provides a fully functional and stable SPA, DMU, and ZVOL layer.
3)LZFS – a Linux kernel module which provides the necessary POSIX layer.

Pieces #1 and #2 have been available for a while and are derived from code taken from the ZFS on Linux project found here. The folks at KQ Infotech are really building on that and providing piece #3, the missing POSIX layer.

Only time will tell how stable the code really is, my opinion at this point is that most software projects have some number of known bugs that exist (and even more have some unknown number of bugs as well), I know I am going to continue to test in a non production environment for the next few months.  At this point I have not experienced any instability (other then what was discussed above) or crashing, all the commands seem to work as advertised, there are a lot of features I have not been able to test yet, such as dedup, compression, etc, so there is lots more to look at in the upcoming weeks.

KQStor’s business model seems to be one where the source code is provided and support is charged for.  So far I have been able to have an open and productive dialog with their developers, and they have been very responsive to my inquiries, however it does not appear that they are going to be setting public tools such as mailing lists or forums, due to their current business model.  I am hoping that this will change in the near future, as I truly believe that everyone will be able to benefit from those kinds of public repositories, and there is no doubt in my mind that such tools will only lead to a more stable product in the long run.

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