Date: Sat, 17 Nov 2012 16:42:48 -0800 From: je <je@8192.net> To: freebsd-fs@freebsd.org Subject: ZFS behavior with odd-number of non-parity drives? Message-ID: <50A82F08.8010908@8192.net>
next in thread | raw e-mail | index | archive | help
Given an odd number of data (non-parity) drives, how does ZFS write data to the individual disks? For example, a 4-drive RAIDZ or 5-drive RAIDZ2 would use three drives for data and two for parity when writing. Since the recordsize is a power of two (and no power of two is evenly divisible by three), it is impossible to write a full sector (be it a 512b or 4k sector) of data to each data drive. In this case, what does ZFS do? Will it write recordsize/3 bytes of data to each drive, leaving the drive to do a read/modify/write operation? Or will ZFS round the write up to the nearest drive sector size and "waste" the extra bytes? I see the best practice for RAIDZ is to use an odd number of drives, and for RAIDZ2 an even number, but I am curious as to the behavior of ZFS in these sub-optimal conditions. John
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?50A82F08.8010908>