Hi, First of all, my apologies for some of my posts appearing 2 or even 3 times here, the forum seems to be acting up, and although I received a Java exception for those double postings and they never appeared yesterday, apparently they still made it through eventually.
Back on topic: I fruitlessly tried to extract higher write speeds from the Seagate drives using an Addonics Silicon Image 3124 based SATA controller. I got exactly the same 21 MB/s for each drive (booted from a Knoppix cd). I was planning on contacting Seagate support about this, but in the mean time I absolutely had to start using this system, even if it meant low write speeds. So I installed Solaris on a 1GB CF card and wanted to start configuring ZFS. I noticed that the first SATA disk was still shown with a different label by the "format" command (see my other post somewhere here). I tried to get rid of all disk labels (unsuccessfully), so I decided to boot Knoppix again and zero out the start and end sectors manually (erasing all GPT data). Back to Solaris. I ran "zpool create tank raidz c1t0d0 c1t1d0 c1t2d0" and tried a dd while monitoring with iostat -xn 1 to see the effect of not having a slice as part of the zpool (write cache etc). I was seeing write speeds in excess of 50MB/s per drive! Whoa! I didn't understand this at all, because 5 minutes earlier I couldn't get more than 21MB/s in Linux using block sizes up to 1048576 bytes. How could this be? I decided to destroy the zpool and try to dd from Linux once more. This is when my jaw dropped to the floor: [EMAIL PROTECTED]:~# dd if=/dev/zero of=/dev/sda bs=4096 ^[250916+0 records in 250915+0 records out 1027747840 bytes (1.0 GB) copied, 10.0172 s, 103 MB/s Finally, the write speed one should expect from these drives, according to various reviews around the web. I still get a healthy 52MB/s at the end of the disk: # dd if=/dev/zero of=/dev/sda bs=4096 seek=183000000 dd: writing `/dev/sda': No space left on device 143647+0 records in 143646+0 records out 588374016 bytes (588 MB) copied, 11.2223 s, 52.4 MB/s But how is it possible that I didn't get these speeds earlier? This may be part of the explanation: [EMAIL PROTECTED]:~# dd if=/dev/zero of=/dev/sda bs=2048 101909+0 records in 101909+0 records out 208709632 bytes (209 MB) copied, 9.32228 s, 22.4 MB/s Could it be that the firmware in these drives has issues with write requests of 2048 bytes and smaller? There must be more to it though, because I'm absolutely sure that I used larger block sizes when testing with Linux earlier (like 16384, 65536 and 1048576). It's impossible to tell, but maybe there was something fishy going on which was fixed by zero'ing parts of the drives. I absolutely cannot explain it otherwise. Anyway, I'm still not seeing much more than 50MB/s per drive from ZFS, but I suspect the 2048 VS 4096 byte write block size effect may be influencing this. Having a slice as part of the pool earlier perhaps magnified this behavior as well. Caching or swap problems are certainly no issues now. Any thoughts? I certainly want to thank everyone once more for your co-operation! Greetings, Pascal This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
