Sun has implemented a file system called ZFS. This file system is optimised for handling large amounts of data. It includes a Logical Volume Manager. It also includes a feature called RAID-Z. It avoids the problem called "RAID 5 write hole" because it has a copy-on-write policy: It does not overwrite the data directly, but writes new data in a new location on the disk. When the write was successful, the old data is deleted. It avoids the need for read-modify-write operations for small writes, because it only writes full-stripes. Small blocks are mirrored instead of parity protected, which is possible because the file system knows the way the storage is organised. It can therefore allocate extra space if necessary. There is also "RAID-Z2" which uses two forms of parity to achieve results similar to RAID 6: the ability to survive up to two drive failures without losing data.