Freebsd – Allowed and safe characters for ZFS filesystem in FreeBSD

freebsdmountzfs

Which characters are allowed and safe for ZFS file system name? Are this characters only ASCII or UTF-8 is supported?

'@' is not allowed because it is reserved for snapshots.

PS: I play with FreeBSD 8.2, 9-RC1 and CURRENT+

Best Answer

Only alphanumeric characters, space*, "-", "_", "." and ":" are accepted for file systems names (and other datasets) under ZFS. The maximum file system name length is 255 characters.

Note that this limitation can easily be "workarounded" by setting a valid directory name as a mount point. The latter can be an unlimited sequence of any character from any Unicode character set and is including "@". Of course, "/" is still forbidden being the path delimiter and "null" is excluded as being the string termination character.

Note that space is not documented as allowed but is accepted anyway. I wouldn't recommend using it anyway as it would possibly break tools.

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You have read the ZFS Tuning Guide, right?

Early versions of ZFS had more than a few issues with memory management, especially when using the dedupe and/or compression options. For the longest time, a simple recipe for ZFS hangs was to set compression=gzip and start copying data. Later versions of ZFS are much better. If you can, you should upgrade to FreeBSD 8.4 or 9.1.

I have a very comparable system at home (16GB RAM, 2 x 3TB SATA disks in ZFS mirror) that's been rock solid since upgrading to FreeBSD 9.1. I have compression enabled and these settings in /boot/loader.conf:

# attempts to get ZFS more stable
vfs.zfs.arc_max="4096M"
kern.maxvnodes=250000
vfs.zfs.prefetch_disable=1
vm.kmem_size="1024M"
vm.kmem_size_max="1024M"

Another thing to check is your motherboard settings for the SATA ports. Initially, my motherboard had the SATA ports set to IDE mode and performance under ZFS was awful, making the memory exhaustion issues worse. After switching them to AHCI mode, the disks perform quite well.

FreeBSD + ZFS + Encryption? Alternatives? Suggestions

You should be able to use one of the geom providers for encryption with ZFS, but you should encrypt the devices below the ZFS. I'd probably setup geli and then make a gpt partition inside of type freebsd-zfs and then go from there.

I recommend you actually test both solutions (freebsd and linux) and decide based on sys admin time and performance which makes sense for you.

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