Hello, all! Here is the patch which adds in ZFS feature to physically reserve space for files, i.e. thick provision
http://cr.illumos.org/~webrev/DKOI/reservation/ The patch adds a new IOCTL for files residing on ZFS filesystems, which performs reservation. The reservation is done by emulating writes for the whole range which need to be reserved, except leaf blocks are not physically written - they are allocated and the blockpointers, which point to them, are marked to be reserved. For marking, the currently unused in illumos 61th bit is used. Tests show at least 4 times speed up of providing thick files comparing to sequential writes of zero blocks. Thanks, Daniil Lunev
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