For some damn reason I thought of a fractal disk arm, an arm that had a >fractal structure, the disk rotates, but the fractal arm can read from
many places at once? Try not to flame me too much. ;^)
According to Chris M. Thomasson <[email protected]>:
For some damn reason I thought of a fractal disk arm, an arm that had a
fractal structure, the disk rotates, but the fractal arm can read from
many places at once? Try not to flame me too much. ;^)
Dunno about fractal, but I have used head per track disks with a fixed arm with many heads, and a disk with a crooked Y-shaped arm with two heads over two tracks.
None of them could do more than one transfer at a time but I
think that was a limit of the electronics of the era, not a fundamental issue.
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Hmmm, hard to believe it makes commercial sense: if you need higher >performance, when would this be price-competitive with an SSD?
Also, that page is very light on details, but the image they include
suggests the two actuators are used on separate platters, so it's akin
to cramming a 2-disk-RAID0 into a single HDD enclosure.
On 5/26/2025 10:42 AM, John Levine wrote:
According to Chris M. Thomasson <[email protected]>:
For some damn reason I thought of a fractal disk arm, an arm that had a
fractal structure, the disk rotates, but the fractal arm can read from
many places at once? Try not to flame me too much. ;^)
Dunno about fractal, but I have used head per track disks with a fixed arm >> with many heads, and a disk with a crooked Y-shaped arm with two heads over >> two tracks.
Yup. And IIRC the IBM 3380 had a linear actuator with two heads per
arm, one covering the outer cylinders, the other the inner cylinders.
The tradeoff was shorter seeks, thus smaller seek time but higher cost
due to more heads.
But if you mean two simultaneous
transfers into a buffer in order to get higher host transfer rate, that
is apparently now available.
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Hmmm, hard to believe it makes commercial sense: if you need higher performance, when would this be price-competitive with an SSD?
Also, that page is very light on details, but the image they include
suggests the two actuators are used on separate platters, so it's akin
to cramming a 2-disk-RAID0 into a single HDD enclosure.
Maybe part of the gain of having two actuators is that each actuator is
a bit lighter?
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 10:42 AM, John Levine wrote:
According to Chris M. Thomasson <[email protected]>:
For some damn reason I thought of a fractal disk arm, an arm that had a >>>> fractal structure, the disk rotates, but the fractal arm can read from >>>> many places at once? Try not to flame me too much. ;^)
Dunno about fractal, but I have used head per track disks with a fixed arm >>> with many heads, and a disk with a crooked Y-shaped arm with two heads over >>> two tracks.
Yup. And IIRC the IBM 3380 had a linear actuator with two heads per
arm, one covering the outer cylinders, the other the inner cylinders.
The tradeoff was shorter seeks, thus smaller seek time but higher cost
due to more heads.
Burroughs had some memorex-built drives that had multiple actuators which allowed it to sustain two simultaneous independent transfers from the
media.
This was circa 1988. The drives were often shared between two
to four systems in loosely coupled multiprocessor configurations.
Ah, what's old is new again....
I can't imagine why Seagate calls that "The world's first multiactuator technology",
given we had it four decades ago.
On 5/26/2025 1:31 PM, Scott Lurndal wrote:
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 10:42 AM, John Levine wrote:
According to Chris M. Thomasson <[email protected]>:
For some damn reason I thought of a fractal disk arm, an arm that had a >>>>> fractal structure, the disk rotates, but the fractal arm can read from >>>>> many places at once? Try not to flame me too much. ;^)
Dunno about fractal, but I have used head per track disks with a fixed arm >>>> with many heads, and a disk with a crooked Y-shaped arm with two heads over
two tracks.
Yup. And IIRC the IBM 3380 had a linear actuator with two heads per
arm, one covering the outer cylinders, the other the inner cylinders.
The tradeoff was shorter seeks, thus smaller seek time but higher cost
due to more heads.
Burroughs had some memorex-built drives that had multiple actuators which
allowed it to sustain two simultaneous independent transfers from the
media.
Interesting. I presume that the two transfers had to be to two
different head of string/controllers.
This was circa 1988. The drives were often shared between two
to four systems in loosely coupled multiprocessor configurations.
That makes sense. No need to mess with the OS to allow two transfers
to/from the same drive.
Ah, what's old is new again....
I can't imagine why Seagate calls that "The world's first multiactuator technology",
given we had it four decades ago.
Come on, Scott! Both of us old codgers learned long ago to separate >Marketing from reality! :-) I'll bet 1988 was before many of Seagate's >people were born, much less involved in the industry.
On 5/26/2025 11:58 AM, Stefan Monnier wrote:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Hmmm, hard to believe it makes commercial sense: if you need higher
performance, when would this be price-competitive with an SSD?
It should be not much more costly than a single disk of the same
capacity. It has the same number of heads, platters, and of course the
same enclosure, etc. A little more work to separate the two arm
magnetic actuators. The same electronics, except for, and this is
probably the most expensive part, an additional read channel. So still
a lot cheaper than an SSD.
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
Hmmm, hard to believe it makes commercial sense: if you need higher
performance, when would this be price-competitive with an SSD?
Also, that page is very light on details, but the image they include
suggests the two actuators are used on separate platters, so it's akin
to cramming a 2-disk-RAID0 into a single HDD enclosure.
The data sheet says it is in effect two 7TB disks in a single enclosure.
It seems to have come and gone. Nobody has them new, refurbished are
$150 - $200 on eBay. An SSD of similar size is in the $2000 range so
it would have made sense for a data warehouse.
On 5/26/2025 12:19 PM, John Levine wrote:[...]
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
I believe you about its current state, but I wonder
why it wasn't more successful. It seems like a big improvement in
throughput for very little extra cost.
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:[...]
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
I believe you about its current state, but I wonder
why it wasn't more successful. It seems like a big improvement in
throughput for very little extra cost.
It seems that the technology is still on offer, e.g.
https://geizhals.eu/seagate-exos-x-2x18-18tb-st18000nm0272-a2883003.html
As for the price (and ignoring offers that are not in stock, or where
the offers vary wildly vary):
EUR Drive
427 Seagate Exos X - 2X18 18TB (2x9TB)
350 Exos X X18 18TB
440 2xToshiba N300 NAS Systems 10TB (total 20TB)
330 2xSeagate Exos E - 7E10 8TB (total 16TB)
385 10TB HDD + 8TB HDD (total 18TB)
So you pay almost as much as for 2 10TB drives, but get only 2 9TB
drives in one enclosure. The power consumption may be better for the
2X18 drive, though.
On 5/27/2025 1:34 AM, Anton Ertl wrote:[...]
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
It should draw less power and require less cooling;
one drive motor versus two
and except for the read channel, half the
electronics.
Stephen Fuld <[email protected]d> writes:
On 5/27/2025 1:34 AM, Anton Ertl wrote:[...]
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
It should draw less power and require less cooling;
one drive motor versus two
Probably not for that reason, but because with two drives there are 4
case housing walls parallel to rotating platters (resulting in more friction) rather than 2 walls for the 2x18 drive.
and except for the read channel, half the
electronics.
The fact that this is presented as two drives to the system makes me
suspect that the drive electronics is duplicated.
On 5/27/2025 9:19 AM, Anton Ertl wrote:[...]
Stephen Fuld <[email protected]d> writes:
On 5/27/2025 1:34 AM, Anton Ertl wrote:
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
The fact that this is presented as two drives to the system makes me
suspect that the drive electronics is duplicated.
Not two drives, but two Logical Units (LUNS).
It's not two separate
drives because there is only one host interface.
So, without knowing for sure, I think the disk has one set of host
interface electronics, one main CPU, one DRAM buffer, one motor control,
etc. It says that it can transfer from both disks (presumably at least
one to/from the buffer) simultaneously, so it has two disk read channels
and two disk write channels. But I don't think anything else is duplicated.
Stephen Fuld <[email protected]d> writes:[...]
On 5/27/2025 9:19 AM, Anton Ertl wrote:
Stephen Fuld <[email protected]d> writes:
On 5/27/2025 1:34 AM, Anton Ertl wrote:
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
to get the project done quickly, they started out by
duplicating the drive electronics (only one motor controller is
connected, and (wild guess) spindown on idle is disabled; otherwise
they would need to synchronize that; or maybe they do, at least in
order to implement staggered spin-up); they added a front end that
provides a common host interface with the two LUNs (probably available
as off-the-shelf component), and the only new development necessary
for the project was the split actuator. That's how it came out for
the 2X14 drive; and my guess is that the sales numbers were good
enough to respin it as 2X18 when the density per platter had increased
enough for that, but not good enough to perform the development of the >original plan.
While the minimal-duplication approach would be cheaper if enough
units are sold, my guess is that the number of 2X drives sold is not
high enough for that, and so it's cheaper to use two mass-produced
drive electronics and one mass-produced LUN-splitter instead.
The fact that the idle power consumption of the 2X14 (7W) is higher
than the idle power consumption of the X14 (5W) >(<https://www.storagereview.com/news/seagate-exos-2x14-hdd-delivers-524mb-s> >is another hint that there probably is more rather than less
duplication.
Stephen Fuld <[email protected]d> writes:
On 5/27/2025 9:19 AM, Anton Ertl wrote:[...]
Stephen Fuld <[email protected]d> writes:
On 5/27/2025 1:34 AM, Anton Ertl wrote:
Stephen Fuld <[email protected]d> writes:
On 5/26/2025 12:19 PM, John Levine wrote:
According to Stefan Monnier <[email protected]>:
Stephen Fuld [2025-05-26 11:16:25] wrote:
https://www.seagate.com/innovation/multi-actuator-hard-drives/
The fact that this is presented as two drives to the system makes me
suspect that the drive electronics is duplicated.
Not two drives, but two Logical Units (LUNS).
<https://www.techopedia.com/definition/321/logical-unit-number-lun> says: |The term LUN was initiated from the SCSI protocol and provided a |methodology for identifying specific disc drives within a regular
|component such as a disc array.
In the present context: If the drive electronics has the minimum
amount of duplication, why present the thing as two LUNs?
It's not two separate
drives because there is only one host interface.
In the scenario described above, disk arrays have only one host
interface but still contain separate drives, each drive identified by
a LUN.
So, without knowing for sure, I think the disk has one set of host
interface electronics, one main CPU, one DRAM buffer, one motor control,
etc. It says that it can transfer from both disks (presumably at least
one to/from the buffer) simultaneously, so it has two disk read channels
and two disk write channels. But I don't think anything else is duplicated.
In that case, why have two LUNs? It seems to me that in this
scenario, it would be easier to use the drive as one 18TB LUN, no need
for the user to arrange the two LUNs into a RAID0 or JBOD.
In this
scenario the drive electronics could arrange the sectors of logically consecutive tracks to come from alternating actuators, which allows to
double the sequential speed, and also to double the IOPS of random
accesses given enough concurrent requests.
My guess is that the eventual intent of Seagate was to provide that
scenario, but to get the project done quickly, they started out by duplicating the drive electronics (only one motor controller is
connected, and (wild guess) spindown on idle is disabled; otherwise
they would need to synchronize that; or maybe they do, at least in
order to implement staggered spin-up); they added a front end that
provides a common host interface with the two LUNs (probably available
as off-the-shelf component), and the only new development necessary
for the project was the split actuator. That's how it came out for
the 2X14 drive; and my guess is that the sales numbers were good
enough to respin it as 2X18 when the density per platter had increased
enough for that, but not good enough to perform the development of the original plan.
Counterevidence for my theory: The Exos X drives are all listed as
having 256MB of cache, including the 2X drives. If the electronics
were fully duplicated, they could list 512MB.
You only get double the IOPS if the host supports command queuing.
As to whether to interleave the addresses, that is an independent
question. There are advantages and disadvantages, mainly revolving
around (pun intended) how long the average user request is versus what
is the unit of interleave.
Stephen Fuld [2025-05-28 08:46:26] wrote:
You only get double the IOPS if the host supports command queuing.
I'd expect that command queuing is the only case that really matters in practice.
As to whether to interleave the addresses, that is an independent
question. There are advantages and disadvantages, mainly revolving
around (pun intended) how long the average user request is versus what
is the unit of interleave.
That seems like a more important benefit: the users get to choose how to spread their data depending on their specific use case.
According to Stefan Monnier <[email protected]>:[...]
Hmmm, hard to believe it makes commercial sense: if you need higher >>performance, when would this be price-competitive with an SSD?
It seems to have come and gone. Nobody has them new, refurbished are
$150 - $200 on eBay. An SSD of similar size is in the $2000 range so
it would have made sense for a data warehouse.
On 5/28/2025 9:08 AM, Stefan Monnier wrote:
That seems like a more important benefit: the users get to choose how toI don't disagree, though I didn't see any mechanism for the user to specify the unit of interleave. Of course you could do this in the host
spread their data depending on their specific use case.
file system.
Stephen Fuld [2025-05-28 09:20:27] wrote:
On 5/28/2025 9:08 AM, Stefan Monnier wrote:
That seems like a more important benefit: the users get to choose how to >>> spread their data depending on their specific use case.I don't disagree, though I didn't see any mechanism for the user to specify >> the unit of interleave. Of course you could do this in the host
file system.
If they appear as two LUNs, then the drive can't do the interleaving,
only the host can.
On 5/28/2025 9:52 AM, Stefan Monnier wrote:
If they appear as two LUNs, then the drive can't do the interleaving,Of course the drive can. In general, you have no idea of the mapping
only the host can.
between what the host calls a LUN/LBA (logical block address), and the physical cylinder and head on the drive.
Stephen Fuld [2025-05-28 10:15:14] wrote:
On 5/28/2025 9:52 AM, Stefan Monnier wrote:
If they appear as two LUNs, then the drive can't do the interleaving,Of course the drive can. In general, you have no idea of the mapping
only the host can.
between what the host calls a LUN/LBA (logical block address), and the
physical cylinder and head on the drive.
Right, but what would be the point of exposing two LUNs if the drive
does the interleaving? Wouldn't it be "all cost, no benefit"?
On 5/28/2025 11:16 AM, Stefan Monnier wrote:
Stephen Fuld [2025-05-28 10:15:14] wrote:
On 5/28/2025 9:52 AM, Stefan Monnier wrote:
If they appear as two LUNs, then the drive can't do the interleaving,Of course the drive can. In general, you have no idea of the mapping
only the host can.
between what the host calls a LUN/LBA (logical block address), and the
physical cylinder and head on the drive.
Right, but what would be the point of exposing two LUNs if the drive
does the interleaving? Wouldn't it be "all cost, no benefit"?
The benefit of LUNs is to allow the host issue more than one command at
a time when the host doesn't support command queuing. It is independent
of the interleaving decision.
On Wed, 28 May 2025 20:37:44 +0000, Stephen Fuld wrote:
On 5/28/2025 11:16 AM, Stefan Monnier wrote:
Stephen Fuld [2025-05-28 10:15:14] wrote:
On 5/28/2025 9:52 AM, Stefan Monnier wrote:
If they appear as two LUNs, then the drive can't do the interleaving, >>>>> only the host can.Of course the drive can. In general, you have no idea of the mapping >>>> between what the host calls a LUN/LBA (logical block address), and the >>>> physical cylinder and head on the drive.
Right, but what would be the point of exposing two LUNs if the drive
does the interleaving? Wouldn't it be "all cost, no benefit"?
The benefit of LUNs is to allow the host issue more than one command at
a time when the host doesn't support command queuing. It is independent
of the interleaving decision.
Seems to me that SR-IOV provides the mechanism to have almost any number
of in-order queues, each; give GuestOS[5] k virtual FUs to device[19].
In the present context: If the drive electronics has the minimum
amount of duplication, why present the thing as two LUNs?
On 5/28/2025 11:16 AM, Stefan Monnier wrote:
Stephen Fuld [2025-05-28 10:15:14] wrote:The benefit of LUNs is to allow the host issue more than one command at
On 5/28/2025 9:52 AM, Stefan Monnier wrote:Right, but what would be the point of exposing two LUNs if the drive
If they appear as two LUNs, then the drive can't do the interleaving,Of course the drive can. In general, you have no idea of the mapping
only the host can.
between what the host calls a LUN/LBA (logical block address), and the
physical cylinder and head on the drive.
does the interleaving? Wouldn't it be "all cost, no benefit"?
a time when the host doesn't support command queuing. It is independent of the interleaving decision.
On Wed, 28 May 2025 20:37:44 +0000, Stephen Fuld wrote:
On 5/28/2025 11:16 AM, Stefan Monnier wrote:
Stephen Fuld [2025-05-28 10:15:14] wrote:
On 5/28/2025 9:52 AM, Stefan Monnier wrote:
If they appear as two LUNs, then the drive can't do the interleaving, >>>>> only the host can.Of course the drive can. In general, you have no idea of the mapping
between what the host calls a LUN/LBA (logical block address), and the >>>> physical cylinder and head on the drive.
Right, but what would be the point of exposing two LUNs if the drive
does the interleaving? Wouldn't it be "all cost, no benefit"?
The benefit of LUNs is to allow the host issue more than one command at
a time when the host doesn't support command queuing. It is independent
of the interleaving decision.
Seems to me that SR-IOV provides the mechanism to have almost any number
of in-order queues, each; give GuestOS[5] k virtual FUs to device[19].
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