> I wonder if it is a real problem, ie, for example cause longer backup > time, will it be addressed in future?
It doesn't cause longer backup time, as long as you're doing a "zfs send | zfs receive" But it could cause longer backup time if you're using something like tar. The only way to "solve" it is to eliminate copy on write (negating the value of ZFS), or choose to pay the price during regular operation, resulting in an overall slower system. You can expect it won't be changed or addressed in any way. You can also expect you'll never be able to detect or measure this as a performance problem that you care about. ZFS and copy on write are so much faster at other things, such as backups, and add so much value in terms of snapshots and data reliability ... There is a special case where the performance is lower. I don't mean to disrespect the concerns of anybody who is affected by that special case. But I believe it's uncommon. > So I should ask anther question: is zfs suitable for an environment > that has lots of data changes? I think for random I/O, there will be no > such performance penalty, but if you backup a zfs dataset, must the > backup utility sequentially read blocks of a dataset? Will zfs dataset > suitable for database temporary tablespace or online redo logs? Yes, ZFS is great for environments that write a lot, and do random writes a lot. There is only one situation where the performance is lower, and it's specific: * You write a large amount of sequential data. * Then you randomly write a lot *inside* that large sequential file. * Then you sequentially read the data back. Performance is not hurt, if you eliminate any one of those points. * If you did not start by writing a large file in one shot, you won't have a problem. * If you do lots of random writes, but they're not in the middle of a large sequential file, you won't have a problem. * If you always read or write that file randomly, you won't have a problem. * The only time you have a problem is when you sequentially read a large file that previously had many random writes in the middle. Even in that case, the penalty you pay is usually small enough that you wouldn't notice. But it's possible. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
