On 26-Jan-07, at 11:34 PM, Pawel Jakub Dawidek wrote:
Hi.
What do you guys think about implementing 'zfs/zpool rewrite' command?
It'll read every block older than the date when the command was
executed
and write it again (using standard ZFS COW mechanism, simlar to how
resilvering works, but the data is read from the same disk it is
written to).
I see few situations where it might be useful:
1. My file system is almost full (or not) and I'd like to enable
compression on it. Unfortunately compression will work from now on and
I'd also like to compress already stored data. Here comes 'zfs
rewrite'!
2. I was bad boy and turned off checksuming. Now I suspect something
corrupts my data and I'd really like to checksum everything. Ok, here
comes 'zfs rewrite'!
In this case you deserve what you get.
3. I created file system with huge amount of data, where most of the
data is read-only. I change my server from intel to sparc64 machine.
Adaptive endianess only change byte order to native on write and
because
file system is mostly read-only, it'll need to byteswap all the time.
And here comes 'zfs rewrite'!
Why would this help? (Obviously file data is never 'swapped').
--T
4. Not sure how ZFS traverse blocks tree, if it is done based on
files,
it my be used to move data from one file closer to each other, which
will reduce seek times. Because of the way how ZFS works, the data may
become fragmented and 'zfs rewrite' could be used for defragmentation.
5. Once file system encryption is implemented, this mechanism can be
used to encrypt existing file system and also it can be used to change
encryption key.
What do you think?
--
Pawel Jakub Dawidek http://www.wheel.pl
[EMAIL PROTECTED] http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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