On Sun, Jan 31, 2010 at 01:59:47PM -0700, David Alexander wrote: > On Sat, 30 Jan 2010 08:50:09 +0000, "Poul-Henning Kamp" > <[email protected]> wrote: > > >In message <[email protected]>, Bob Camp writes: > > > >>> Don't get an SSD thinking you're going to get speed. The 5501 will > >>> limit the throughput well below what you'd expect for an SSD. > > > >An SSD still does miracles for access time. > > Yes it does. I should have mentioned that the one thing that drove me > to buy the SSD was how poorly my CF card handled multiple simultaneous > requests. For example, when I open my email client it syncs all the > folders with the IMAP server in parallel. This was painfully slow on > the CF card which is designed to read or write a single file at a > time. Switching to the SSD made a significant improvement in parallel > operations.
As a rule of thumb: buy media based on SLC and not MLC flash. Technically it is something different and I have been seen MLC cards without this problem, but I've also seen that productions silently changed and the next bunch of the same card is slow. Many cheap cards today have the problem that they just care to be fast when writing linear in large chunks, which is Ok for cameras using msdosfs to write large pictures. I think the real reson behind is a simplified wear leveling technik. I've seen MLC cards degrading down to less than 10 transactions per second, which is really painfull if the OS decides to flush buffers. Another rule of thumb is that flash blocks are in the 4k or 8k range. If you write smaller chunks the card is doing read modify write cycles. Moreover I noticed that it is horribly slow to write to the same physical block again, so writing continuous 8k in two 4k chunks is a very bad strategy. This is also true for SLC cards, but they don't undergo that heavy speed penalty as some MLC cards do. Use a big and properly aligned filesystem blocksize and you should see much better results. -- B.Walter <[email protected]> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm. _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
