ZFS

ZFS is a combined file system and logical volume manager created by Sun Microsystems. For more official information see: Wikipedia ZFS Entry This means that not only is ZFS a file system but it also functions as a software raid. While ZFS has many features and is a solution for things such as the RAID 5 write hole it is also extremely simplistic. ZFS is easy, fast, flexible, and under development.

ZFS Usable OS's:

• Solaris (Suns main OS no longer free but just a trial version)
• OpenSolaris (Suns opensource OS)
• FreeBSD (ZFS is being ported to this OS and while it is stable it lags behind the Solaris release for obvious reasons)
• Nexenta (This OS claims to be the Solaris kernel with the Ubuntu (Linux) userland which seems nice but it has no window manager by default)
• StormOS (This OS is the same as Nexenta but has GNOME installed by default)

ZFS Background

During my research I found some of the information on ZFS confusing and have decided that it was for two reasons. The first was that it is still relatively new and people have many different questions about it. The second is that from its development it seems to have undergone a lot of changes. Even when I went on Freenode and was in the #ZFS IRC room and asking questions about it I was getting opinionated answers and no solid fact from some of the people using ZFS.

From what I have managed to gather ZFS likes and is used most with whole disks. It can be used with slices (the term for partitions in BSD and Solaris) and even files. Files to me was the most interesting because it allows one to experiment and understand ZFS without destroying anything and also allows one interesting opportunities if they see fit. Like completely ignoring performance and utilising the full sizes of disks. Like RAID ZFS can't use different size disks but takes the size of the smallest and applies that max size to all your drives. I think it is a limitation that ZFS should overcome but one step at a time I suppose.

As far as commands go try 'man zpool' etc and look at the links at the bottom of the page.

ZFS Possibilities + A Poor Man's Raid

Like I said though ZFS can use files and slices. That is I could divide drives into whatever size I want and use them how I please. With files and slices, though, one loses performance because of write caching issues which are enabled by default with whole disks but not with this method. You could have two 1 terrabyte drives and 1 500GB Drive and have 1.5 Terrabytes of usable space. That is you would use the Raid 2 level of ZFS and divide all the drives into 500GB slices or files.

Raid 5 or raidz (as ZFS calls it) Equation from 'man zpool':

A raidz group with N disks of size X with P parity disks can hold approximately (N-P)*X bytes and can withstand P device(s) failing before data integrity is compromised. The minimum number of devices in a raidz group is one more than the number of parity disks. The recommended number is between 3 and 9 to help increase performance.

Ex:

If you have 5 500GB drives or 2x 1TB drives and 1X 500GB which are divided into slices or files you would be fine if any one drive failed.

(5-2)*500GB = 1.5 Terrabytes

This has the redundancy of 2x 500gb drives. So if one terrabyte drive failed you would be fine but have no redundancy.

You could do this but currently ZFS would not perform optimal (3-5x supposedly) and it may be simpler just to by more drives. Still. From reading this one can see what is possible with ZFS. One could even build a Poor Man's Raid with this and still be safe. The only considerations are the performance of this raid. Slices seem to be easy to use if they are not part of a root ZFS filesystem and with files one has to worry about outside data corruption of the files and possible outside config issues.

The way ZFS was 'ment' to be used is with full disks. It enables HD write caching by default and is extremely simple in most cases. It is as simple as finding out your device names and doing 'zpool create mirrorname mirror devicename1 devicename2' or 'zpool create mirrorname mirror filepathname1 filepathname2' or 'zpool create raidmirror raidz file/device/slicename file/device/slicename' on any system with ZFS installed. The 'device' that ZFS creates will be located at /mirrororraidname/ on the root filesystem.

ZFS Misc Notes

In OpenSolaris format -e or just format will give you your device names. Also when using entire drives with ZFS and you are not root it will not find the devices. su and then issue the command. You should be fine.

ZFS also has its own share maker. That is the zfs command creates your NFS or CIFS shares...look it up.

ZFS Resources

[1] - Great for beginners. Lets one understand how to use ZFS without having any spare hard drives.

[2] - Turning a ZFS mirror into a raidz array.

[3] - Official ZFS Admin Guide Link

[4] - ZFS Command Quick Reference

[5] - ZFS Best Practices Guide

[6] - Open Solaris Mailing Lists

File:ZFS Command Quick Reference.odt - Sun ZFS Command Quick Reference

File:819-5461.pdf - Solaris ZFS Administration Guide