I would echo Jeff's questions about what the use case is here. Is the goal to reserve space for individual files, and doing so physically (as opposed to logically, like filesystem reservations) was the easiest way to implement it? Did you investigate implementing a logical per-file reservation? A logical reservation should perform better (both when setting the reservation, and when writing, since there would be more physical free space).
I think that logically, this is the equivalent of writing zeros to the file. How does this interact with compression? Normally, writing zeros to a compressed file will result in hole blocks being created. Is the idea that this feature is only intended to be used with compression disabled? --matt On Tue, Oct 28, 2014 at 5:20 AM, Daniil Lunev <[email protected]> wrote: > 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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