> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Nathan Kroenert > > That reminds me of something I have been wondering about... Why only 12x > faster? If we are effectively reading from memory - as compared to a > disk reading at approximately 100MB/s (which is about an average PC HDD > reading sequentially), I'd have thought it should be a lot faster than 12x. > > Can we really only pull stuff from cache at only a little over one > gigabyte per second if it's dedup data?
Actually, cpu's and memory aren't as fast as you might think. In a system with 12 disks, I've had to write my own "dd" replacement, because "dd if=/dev/zero bs=1024k" wasn't fast enough to keep the disks busy. Later, I wanted to do something similar, using unique data, and it was simply impossible to generate random data fast enough. I had to tweak my "dd" replacement to write serial numbers, which still wasn't fast enough, so I had to tweak my "dd" replacement to write a big block of static data, followed by a serial number, followed by another big block (always smaller than the disk block, so it would be treated as unique when hitting the pool...) 1 typical disk sustains 1Gbit/sec. In theory, 12 should be able to sustain 12 Gbit/sec. According to Nathan's email, the memory bandwidth might be 25 Gbit, of which, you probably need to both read & write, thus making it effectively 12.5 Gbit... I'm sure the actual bandwidth available varies by system and memory type. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
