It's not defined by POSIX (or Solaris). You can rely on being able to atomically write a single disk block (512 bytes); anything larger than that is risky. Oh, and it has to be 512-byte aligned.
File systems with overwrite semantics (UFS, QFS, etc.) will never guarantee atomicity for more than a disk block, because that's the only guarantee from the underlying disks. File systems with copy-on-write semantics (WAFL, ZFS, etc.) can guarantee atomicity for arbitrarily large writes, but will usually have some limits due to the desire to limit the amount of data which is modified in one transaction. For ZFS, writes to a single "ZFS block" will be atomic. I believe that a 128K write which does not cross a 128K boundary will always be atomic if you have not set a lower record size for the file system, but I haven't studied the code in detail. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
