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 Post subject: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 2nd, 2013, 18:28 
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Location: San Francisco, CA
Is this a good idea, or is there a technical issue I have overlooked?

I would like to understand why hard disk drives are not manufactured with the user data and servo information in a single spiral (a la DVD). Since track-to-track seek is so common, reducing it from 1ms to 0 would be a big deal.

Image

I've researched it and floated it to some other engineers but have not heard from hard drive engineers. In trivialized form, it seems to me you just need to add a sensor to track the platter(s) angle, and then it's just a software problem.

I laid out how I understand the current architecture works and how I imagine a spiral sector architecture would work for comparison.

0) Initial state. Head is over a random track. Ignoring multiple platters and heads. Ignoring sector size. Sectors per track is fixed at 64 (0-63). I don't believe this setup gives an advantage to either data organization architecture, and allows me to simplify a bit.

Read using Conventional Concentric Circle Track Architecture
T1) Receive request for track 300,000 sector 3 through track 300,001 sector 5.
T2) ~6ms Calculation is done using current voice coil position and destination voice coil position. Head accelerated and decelerated to try for track 300,000.
T3) ~1ms (settling time) User data and servo data are read; voice coil is adjusted till we are within tolerance and can trust we know what sector we are reading and its value. If we are on the wrong track we could trivially go back to step 2.
T4) ~8ms (just shy of 1 revolution) Read 61 sectors while adjusting voice coil till we have sectors 3 through 63.
T5) ~0.5ms Head accelerated and decelerated to get over next track.
T6) ~0.5ms User data and servo data are read; voice coil is adjusted till we are within tolerance and can trust we know what sector we are reading and its value.
T7) ~2ms (say a quarter revolution) Read 6 sectors till we have 0 through 5. Since drive data is organized to minimize track-to-track latency, sectors we want are probably in the first few we read, so we don't need to wait for a full revolution.

T total 18ms


Read using Spiral Architecture
S1) Receive request for track 300,000 sector 3 through track 300,001 sector 5.
S2) ~6ms Calculation is done using current voice coil position and destination voice coil position and platter angle. Head accelerated and decelerated to try for spiral sector (300,000*64+3) – (estimate of number of settling time sectors).
S3) ~1ms (settling time) User data and servo data are read; voice coil is adjusted till we are within tolerance and can trust we know what sector we are reading and its value. If we are on the wrong track we could trivially go back to step 2.
S4) ~9ms (just over 1 revolution) Read 67 sectors while adjusting voice coil till we have them all.
(No need for steps 5-7)

S total 16ms

I'm not saying this is typical, it just demonstrates where the time savings the would come from and assigns some labels. For example, during S4, since the voice coil is being adjusted anyway, I assumed the head could be adjusted inward 1/64 of 1/300,000 of an inch per sector (at 300,000 tpi). That might not be true.


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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 2nd, 2013, 20:17 
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Spiral is used during servo write on some HDD's. Go check some patents :D :idea:

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 2nd, 2013, 20:19 
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http://www.google.com/patents/US7688539

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 3rd, 2013, 15:21 
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I wonder if spiral vs. Circular stw'en disks are more or less sensitive to servo damage.
@guru, do you know for sure a model with spiralized stw ? Turning on the DDA...


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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 3rd, 2013, 15:40 
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Joined: April 3rd, 2013, 15:29
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Location: El dorado
Is there a way to get low-level information about possible analogue interface with the heads?
I want to try reading and writing analogue signal on the HDD surface.

Especially i'm intresting about any information of the interface with the internal multiplexer-amplifier chip connected to heads.

Don't know even from which side i should start...

thnx
D


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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 3rd, 2013, 16:46 
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Location: England
Maxtor Apollo N40P.

Mechanical(pushpin) seed servo written concentrically for SA ZONE and then spiral for rest of media.

Then drive will latch onto spiral and build servo. Clever stuff :)

That's why it has two SA zones, original for spiral code and secondary SA copied after full pack servo complete.


WD on Marvel use same idea :)

http://www.me.berkeley.edu/~horowitz/Pu ... onSSTW.pdf. Good read


quote="BlackST"]I wonder if spiral vs. Circular stw'en disks are more or less sensitive to servo damage.
@guru, do you know for sure a model with spiralized stw ? Turning on the DDA...[/quote]

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 4th, 2013, 7:52 
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guru wrote:
Maxtor Apollo N40P.

Mechanical(pushpin) seed servo written concentrically for SA ZONE and then spiral for rest of media.

Then drive will latch onto spiral and build servo. Clever stuff :)

That's why it has two SA zones, original for spiral code and secondary SA copied after full pack servo complete.



Amazing, for a drive of "that" age. Would be nice to see if it is possible to reservo the "pack" (what a pack... 1 platter mono head :D ) using commands of if the drive was designed for spiral servo on data area to last only for the lifetime of the disk and when servo is gone, it's gone (uhm... actually some stuff.... maybe..... :mrgreen:)


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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 4th, 2013, 8:47 
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BlackST wrote:
Would be nice to see if it is possible to reservo the "pack"

If you have STW that could make spirals

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 4th, 2013, 8:49 
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guru wrote:
Maxtor Apollo N40P.

Mechanical(pushpin) seed servo written concentrically for SA ZONE and then spiral for rest of media.

Then drive will latch onto spiral and build servo. Clever stuff :)

it's spirals
Drive then positioning between two spirals (using them as A and B) writes servo, erasing spirals

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 5th, 2013, 15:53 
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Joined: July 18th, 2006, 3:05
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Doomer wrote:
BlackST wrote:
Would be nice to see if it is possible to reservo the "pack"

If you have STW that could make spirals


Not necessarily by means of external STW. I have some problems with PMs both receiving and sending, maybe it's this handy. I'm PMing you, if you can read (or not) please confirm.


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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 5th, 2013, 16:11 
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BlackST wrote:
I'm PMing you, if you can read (or not) please confirm.

For some reason I cannot

Update: Now I can. Got your PM, replied

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 8th, 2013, 5:42 
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Joined: April 26th, 2012, 1:52
Posts: 392
Location: Chicago, USA
This would be useful only for long sequential reads of several hundred MB or more. And only after the disk has finished all the metafile and housekeeping seeks related to getting ready to begin a long read operation.

And once random access enters the picture you're back down to jumping all over the place again.

With solid state ram buffers and other system latencies, this small advantage gets washed away.

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 Post subject: Re: Spiral Layout for Hard Disk Drive Sectors
PostPosted: April 8th, 2013, 18:14 
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Joined: April 2nd, 2013, 17:34
Posts: 2
Location: San Francisco, CA
Keatah,

At an average of 500K bytes per track with 4 heads,
you could expect your first track-to-track (single track) savings as described in my original post
to occur between

(minimum) 1k (two sectors)

to

(maximum) 500K * 4 = 2mb + 1kb (a cylindar plus a sector)

for an average of
~1mb. Not "several hundred MB".


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