On Thu, December 2, 2010 00:14, Miles Nordin wrote: > NTFS has 4KByte allocation units, so all you have to do is make sure > the NTFS partition starts at an LBA that's a multiple of 8, and you > have full performance. Probably NTFS is the reason WD has chosen > 4kByte.
4K wasn't chosen by WD (alone), it was chosen by the trade group IDEMA, of which WD and the other major vendors are a member: http://idema.org/_smartsite/external/bigsector/about.php IDEMA then reported into T13 (the (S)ATA folks) on their findings. Microsoft obviously needed to be involved as they're probably the largest OS vendor which uses SATA disks for storage. I'm sure T10 (SCSI) was also involved, but they've had non-512 sectors on some of their drives for a while (e.g., 520). I'm sure other sector sizes were discussed, and I'd love to be able to see the discussion on the pros and cons of the other options. > It doesn't matter what sector size the drive presents to the host OS > because you can get the same performance character by always writing > an aligned set of 8 sectors at once, which is what people are trying > to force ZFS to do by adding 3 to ashift. Until you're in a virtualized environment. I believe that in the combination of NetApp and VMware, a 64K alignment is best practice last I head. Similarly with the various stripe widths available on traditional RAID arrays, it could be advantageous for the OS/FS to know it. The other thing is that with the growth of SSDs, if more OS vendors support "dynamic" sectors, SSD makers can have different values for the sector size to allow for performance changes as the technology evolves. Currently everything is hard-coded, but everyone updates things to be dynamic, it could make sense to take advantage of it. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
