ZFS features: RAID-Z

I started slowly building up my knowledge of ZFS, and have decided to start with the most tasty things. One of them is a RAID-Z approach.

Jeff Bonwick – a ZFS author and one of newly created OpenSolaris ZFS community leaders, wrote a wonderful article on RAID-Z where he thoroughly explains what’s new and cool about RAID-Z compared to RAID-5. Please read this masterpiece here.

Cool things about RAID-Z

  1. A traditional weakness of parity-based RAID schemes – write hole – is fixed
  2. There’s quite a performance improvement because now we have dynamic length stripes – any small amount of data will be treated as a data block of a full-stripe size, and therefore it will be immediately and fully written onto disks.
  3. Data integrity improved – in addition to traditional XORs to validate data based on parity knowledge, each RAID-Z block is validated with a 256-bit checksum.
  4. ZFS has a self-healing functionality built-in. If one of data disks returns corrupted data, ZFS restores the correct data with parity, compares checksums to validate the result, returns this correct data to the disk operation which requested it, and fixes corrupted data on the disk which gave us the corrupted data. Must be really useful!

That’s all for now. Soon there will be new ZFS presentations – and I hope they will have even more information on RAID-Z.

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