Hi! > During the testing period of about 5 months I have concluded: > > 1) There are 3 identical Fujitsu RX200 S6 test servers which all show the > same problem, but I also reproduced it on some Sun Fire and Dell server. > > 2) The problem happens with both HW RAID (MegaRAID SAS 2108) and when disks > were directly on integrated SATA card. > > 3) The problem happens with different Kernel versions (tried 3.14, 3.16, > 3.18) > > 4) The problem happens with newest FW/BIOS versions and on older version > > 5) I have checked/replaced the cabling. > > 6) It is not a caching issue (controller/disk caches were off during > testing, but even putting them on had minor impact on the results) > > 7) The problem happens with both 2.5" SATA (12 x HGST Travelstar 1TB, 3 x WD > Black 750G), and SSD disks (3 x Samsung Pro 840) > > 8) I have NOT been able to reproduce it on Windows - the speeds have been > good for all disks at all times. > > 9) Changing the disks (eg. taking currently slow disk and putting it to > another server) has mixed results - it usually triggers some change of speed > (slow becomes fast or vice-versa) but not always. > > > The only thing that somewhat correlates with the change of speed is the > environment: the IO speed of disks is generally better when testing in the > office vs if that exact same server is in the server room. It might just > been luck, however. > I did not find correlation with the uptime, restarts, change of temperature, > etc, so I assumed it might be the vibrations/rotations for SATA disks, but > now that I have reproduced it with expensive SSD disks as well, I am out of > ideas. That's strange. Vibrations? But not for SSDs. Does hwmon say anything interesting? Anything in smart? > Only 20Mbytes/s on SSD must be wrong, right? (Especially if week earlier or > week later it is ~300MBytes/s). Yes. Can you try the disks in different mainboard (but keep software version?) Are there any other performance problems? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
