Will Murnane wrote: > On 9/6/07, Diego Righi <[EMAIL PROTECTED]> wrote: >> ...anyway I wanted to make it the most silent I could, so I suspeded all the >> 10 disks > Warning: unfounded speculation ahead. > > I've heard that this can cause performance issues and undue wear on > the drive. The reasoning is that since the arm assembly accelerates > in one direction, and there's not much force keeping the drive from > rotating, it spins in the opposite direction a little bit. This isn't > a huge problem by itself, but since the place the arm was aiming for > is no longer there due to the counter-rotation, it has to seek a > little bit in the other direction, generating more wear and tear on > the bearings, more heat from the drive, and shorter drive lifetimes.
I was highly skeptical, given that drives are designed to run in both horizontal and vertical orientations (and to switch between them without reformatting, e.g. see <http://www.hitachigst.com/tech/techlib.nsf/techdocs/4236D595E2C5309F862572C500813B89/$file/C10K147_IG.pdf>), and that the forces on the drive arm are quite different depending on the orientation (even though the arm is counterbalanced). However, a little searching turned up <http://www.sidman.com/angaccel.htm>, which tends to support the reasoning above: # Accordingly, known compensation or disturbance rejection systems, while # performing satisfactorily for applications using linear or unbalanced # rotary actuators, fail to address the problems of spindle imbalance # forces, external shock or vibration and windup in systems having a # balanced rotary actuator. This failure is due to the fact that only # angular acceleration of the HDA in the direction of actuator rotation # substantially causes positioning errors in systems that utilize a balanced # rotary actuator. and suggests using an acceleration sensor specifically to compensate for "angular acceleration of the HDA in the direction of actuator rotation". Suspending the drive obviously does change this acceleration. Another possible argument is that if the drive moves slightly, so does the connector to it, which seems like a bad idea. -- David Hopwood <[EMAIL PROTECTED]> _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
