On Thu, May 25, 2006 at 12:01:18AM +0200, Robert Milkowski wrote: > Hello Scott, > > Wednesday, May 24, 2006, 9:42:06 PM, you wrote: > > SD> How does (or does) ZFS maintain sequentiality of the blocks of a file. > SD> If I mkfile on a clean UFS, I likely will get contiguous blocks for my > SD> file, right? A customer I talked to recently has a desire to access > SD> large volumes of sequential data. They were concerned about maintaining > SD> this file as a string of sequential blocks on disk (for performance > SD> reasons) as they update it. > > SD> This brought up the second part of the question - how does ZFS deal with > SD> things that look and feel like directio? When processes update blocks > SD> "in place", like a database might do, are new blocks allocated, or the > SD> existing blocks left alone? If they are left in place, doesn't that > SD> screw around with the transactional nature of ZFS? > > SD> Is this question at all clear? > > "updated" blocks will be actually written to new place - so if you > update random blocks in a file then reading this file sequentially > will not be that sequential.
On the other hand, if you are reading the file sequentially, ZFS has very good read-ahead algorithms. Cheers, - jonathan -- Jonathan Adams, Solaris Kernel Development _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
