Anton B. Rang writes: > >> In our recent experience RAID-5 due to the 2 reads, a XOR calc and a > >> write op per write instruction is usually much slower than RAID-10 > >> (two write ops). Any advice is greatly appreciated. > > > > RAIDZ and RAIDZ2 does not suffer from this malady (the RAID5 write hole). > > 1. This isn't the "write hole". > > 2. RAIDZ and RAIDZ2 suffer from read-modify-write overhead when > updating a file in writes of less than 128K, but not when writing a > new file or issuing large writes. >
I don't think this is stated correctly. All filesystems will incur a read-modify-write when application is updating portion of a block. The read I/O only occurs if the block is not already in memory cache. The write is potentially deferred and multiple block updates may occur per write I/O. This is not RAIDZ specific. ZFS stores files less than 128K (or less than the filesystem recordsize) as a single block. Larger files are stored as multiple recordsize blocks. For RAID-Z a block spreads onto all devices of a group. -r > > 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
