Unix tip: ZFS administration

From the looks of it, ZFS administration is significantly simpler than administration of other complex file systems such as Solaris Disk Suite and Veritas Volume Manager. You can get a lot more done with fewer commands and the chance of making an error that is difficult to back out of is practically non-existent. On the other hand, it's still new to most Unix sysadmins and even those of us who have been working with other Unix file systems such as ufs or efs are going to have to devote some time to getting used to new vocabulary, commands and ways of thinking.

ZFS is without doubt a giant step forward in file system design and is without practical limitations. It features an impressive immunity to the kind of file system corruption that have hounded many of us for decades (refer to my recent problems with "freeing free blocks" crashes). Created by Jeff Bonwick's team at Sun, ZFS is already in use on various Linux, Mac OS X and FreeBSD systems.

128 bit means it can store 18 billion times more data than current 64-bit file systems with a 16 times 2 to the 64 byte maximum file system size which can comprise a single file if you want.

ZFS file systems are built on top of the concept of pools or "zpools" as they are referred to in ZFS. Instead of a volume manager sitting on top of multiple drives and adding a fair degree of complexity, ZFS joins devices into storage pools -- large data stores from which file systems can be built.

With ZFS, you don't have to carefully plan out your partitions and file systems. File systems can easily be grown as needed and new devices can be added at any time, enlarging the space available to all file systems.

Since ZFS is transactional (think "no fsck"), it is always consistent. With journaling, file system changes can be replayed as needed and no external tool is required to effect repairs. Damage caused by incomplete I/O operations just don't happen. Changes are either entirely complete or entirely ignored.

ZFS is also "self-healing". This means that all data, including metadata, are automatically checksummed. In addition, various levels of redundancy, including mirroring and ZFS' own version of RAID-5, called "RAID-Z". If a bad data block is detected, ZFS gets the correct data from a copy and repairs it.

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