On Sun, Dec 13, 2009 at 11:51 PM, Steve Radich, BitShop, Inc. <ste...@bitshop.com> wrote: > I enabled compression on a zfs filesystem with compression=gzip9 - i.e. > fairly slow compression - this stores backups of databases (which compress > fairly well). > > The next question is: Is the CRC on the disk based on the uncompressed data > (which seems more likely to be able to be recovered) or based on the zipped > data (which seems slightly less likely to be able to be recovered). > > Why? > > Because if you can de-dup anyway why bother to compress THEN check? This > SEEMS to be the behaviour - i.e. I
ZFS deduplication is block-level, so to deduplicate one needs data broken into blocks to be written. With compression enabled, you don't have these until data is compressed. Looks like cycles waste indeed, but ... Regards, Andrey > would suspect many of the files I'm writing are dups - however I see high cpu > use even though > on some of the copies I see almost no disk writes. > > If the dup check logic happens first AND it's a duplicate I shouldn't see > hardly any CPU use (because it won't need to compress the data). > > Steve Radich > BitShop.com > -- > This message posted from opensolaris.org > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
