On Thu, 31 Dec 2009, Ragnar Sundblad wrote:
Also, currently, when the SSDs for some very strange reason is constructed from flash chips designed for firmware and slowly changing configuration data and can only erase in very large chunks, TRIMing is good for the housekeeping in the SSD drive. A typical use case for this would be a laptop.
I have heard quite a few times that TRIM is "good" for SSD drives but I don't see much actual use for it. Every responsible SSD drive maintains a reserve of unused space (20-50%) since it is needed for wear leveling and to repair failing spots. This means that even when a SSD is 100% full it still has considerable space remaining. A very simple SSD design solution is that when a SSD block is "overwritten" it is replaced with an already-erased block from the free pool and the old block is submitted to the free pool for eventual erasure and re-use. This approach avoids adding erase times to the write latency as long as the device can erase as fast as the average date write rate.
There are of course SSDs with hardly any (or no) reserve space, but while we might be willing to sacrifice an image or two to SSD block failure in our digital camera, that is just not acceptable for serious computer use.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
