On Aug 24, 12:39 pm, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote:
Is this because less of the disk is actually being used so on a given
platter the head doesn't have such a large range of tracks to move
over?

In order for the effective seek time to be reduced to a quarter the
seeking must be independent. To achieve that I think the striping
would need to be very coarse (eg 512kb or 1Mb).

On Aug 24, 12:39 pm, "Brian Selzer" <br... (AT) selzer-software (DOT) com> wrote:
Is this because less of the disk is actually being used so on a given
platter the head doesn't have such a large range of tracks to move
over?

In order for the effective seek time to be reduced to a quarter the
seeking must be independent. To achieve that I think the striping
would need to be very coarse (eg 512kb or 1Mb).

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.

"David BL" <davidbl (AT) iinet (DOT) net.au> wrote

Yes. And the bit density is generally greater at the outside of the
platter, so it generally takes fewer tracks to store the same information
there as opposed to near the center; consequently, simply dividing the
difference of the full-stroke seek and the track-to-track seek by four is a
perhaps overly conservative method of estimation. I want to stress that
this is not just a hair-brained theory of mine: I've had significant success
using this mechanism to boost performance. In one application, by
installing a disk that was seven times the size required and creating a
partition on the outer edge of the disk, performance improved by over 6000%:
batch processes that had been taking over 25 hours to complete were
finishing in under 25 minutes.

Drives that support disconnection or some other command queueing mechanism
are all that is needed for seeking to be independent.

I think using a coarse stripe is counterproductive. There would be a bigger
chance that a seek in the middle of the read would be required. Consider:
if 3.5 stripes fit on a track in one zone of the disk, then on average every
fourth read would require an additional seek to get the remaining half
stripe. If on the other hand, 28 stripes fit on a track, then no additional
seeks would be necessary. Even if it were 28.5 stripes instead of 28, one
additional seek for every 29 reads is a whole lot better than one for every
4.