MEGAFILE 60 disk capacity issue

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tzok
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MEGAFILE 60 disk capacity issue

Postby tzok » Sun Dec 03, 2017 11:05 am

Some time ago I've bought Digital Data Deicke HD64 (Atari MEGAFILE 60) in an "unknown" condition. Inside there was a Seagate ST277R RLL drive which was apparently dead (ICD reported error #06, which means Track 0 fault). I had a spare and never used NEC D3142 45 MB 3,5" MFM disk and decided to replace dead Seagate with it. Using ICD 6.5.5a I've chosen to initialize the drive, but it was not on a list of supported drives, so I've entered its parameters "by hand".
ICD requires following parameters:
Heads: 8
Cyls: 642
RW:
PC: 128
Zone: 664
Step:
there is no sectors/track field (which for this drive is 17), and I've left RW and Step unfilled as they are optional. I'm sure, I've chosen an MFM, not RLL mode, yet I've ended up with 65MB of space.

Drive is working, surface test went fine. But why this drive has so much higher capacity than nominal?
Last edited by tzok on Sat Dec 09, 2017 8:39 pm, edited 1 time in total.

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Re: MEGAFILE 30 disk capacity issue

Postby czietz » Sun Dec 03, 2017 11:28 am

The controller in the Metafile 30 only supports RLL. That's why you get 1.5 times the capacity. At the expense of the reliability, of course, because a hard disk only specified for MFM might not work correctly with RLL encoded data.

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Re: MEGAFILE 60 disk capacity issue

Postby tzok » Sat Dec 09, 2017 8:51 pm

Actually it is MEGAFILE 60 aka DDD HD64... I've corrected my post, bu it disappeared :/

Datasheet of this NEC D3142 unit says it is an MFM disk with 17 sectors/track, but may be formatted to 26 sectors/track using RLL. I think it may be extremely hard to find a working ST277R disk nowadays. Even if I'd find one, I'm not sure if it would be more reliable than this NEC, which seemed to be an unused unit (I had it for years, together with the WD ISA MFM controller card).

Another problem was the 19 pin cable... I've cut and solder DB-25M plugs to produce DB-19M, and a Centronics cable to get a proper 19+ wires shielded cable. It is not pretty, but at least it works. I have to figure out some covers for the plugs though. I'll probably make some resin mould.

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Re: MEGAFILE 60 disk capacity issue

Postby ijor » Sun Dec 10, 2017 2:11 am

Most MFM drives can work with RLL without problems. RLL uses the same density as MFM. Those MFM drives were manufactured before RLL controllers reached the market. They just weren't factory tested with RLL.

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Re: MEGAFILE 60 disk capacity issue

Postby AtariZoll » Sun Dec 10, 2017 7:40 am

ijor wrote:Most MFM drives can work with RLL without problems. RLL uses the same density as MFM. Those MFM drives were manufactured before RLL controllers reached the market. They just weren't factory tested with RLL.

I don't think that "RLL uses the same density as MFM." is good formulation. Even if flux density (or whatever is proper term) on surface might be same, structure is different.
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.

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Re: MEGAFILE 60 disk capacity issue

Postby ijor » Sun Dec 10, 2017 1:19 pm

AtariZoll wrote:I don't think that "RLL uses the same density as MFM." is good formulation. Even if flux density (or whatever is proper term) on surface might be same, structure is different.


Encoding is of course different by definition. So what? What matters here is the transition density/frequency at the disk surface, and that is the same in both cases. These are bare dumb drives, not much different in this regard than a floppy drive. Unlike later drives with integrated controllers, these drives don't perform any decoding or encoding, so they are not concerned with any density other than the one on the surface.

That is not to say that the encoding doesn't have any relevance at all, it has. A small percentage of MFM drives might not work properly with RLL.

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Re: MEGAFILE 60 disk capacity issue

Postby AtariZoll » Sun Dec 10, 2017 2:48 pm

We need to think on everything - so on not rare case of people who read it just in rush.
They will see only "RLL uses the same density as MFM." - and that can trigger some bad ideas. That's why need to add some more details. Or just to formulate it differently .
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.

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Re: MEGAFILE 60 disk capacity issue

Postby tzok » Wed Dec 27, 2017 8:22 pm

What with a bad sector list? It is given in the form of Head, Cylinder, Bytes from index... but BFI will be different when drive is reformated from MFM (17 sectors/track) to RLL (26 sectors/track). Should I recalculate it in order to enter it during LLF? My drive is NEC D3142, and it has been manufactured in the era of IDE drives... datasheet says "Sectors/Track 17 (RLL = 26 sectors)", so it is RLL aware.

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Re: MEGAFILE 60 disk capacity issue

Postby 1st1 » Thu Dec 28, 2017 8:56 am

Bad track list remains the same, because it does not contain sector numbers, only tracks and heads.

MFM and RRL use the same magnetic density, the difference is the encoding. RLL is 1.5 times more effective than MFM. For further details I recommend to read the "Scheibenkleister" book.
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Re: MEGAFILE 60 disk capacity issue

Postby czietz » Thu Dec 28, 2017 2:15 pm

1st1 wrote:Bad track list remains the same, because it does not contain sector numbers, only tracks and heads.


This is not exactly true; the defect list printed on my MFM HD also contains the location of the defect in "bytes from index mark" (BFI). If I were to format it with RLL, I suppose I would have to multiply the BFI value with 1.5.

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Re: MEGAFILE 60 disk capacity issue

Postby ijor » Thu Dec 28, 2017 3:44 pm

I would recreate the bad sector list if you perform a low level format anyway. May be just run some software that performs a surface test and marks the bad clusters at the high level format.

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Re: MEGAFILE 60 disk capacity issue

Postby 1st1 » Fri Dec 29, 2017 11:01 pm

czietz wrote:
1st1 wrote:Bad track list remains the same, because it does not contain sector numbers, only tracks and heads.


This is not exactly true; the defect list printed on my MFM HD also contains the location of the defect in "bytes from index mark" (BFI). If I were to format it with RLL, I suppose I would have to multiply the BFI value with 1.5.


It's quite difficult to calculate the sector number from the byte offset because you don't know the exact logical structure every controller is using in low level format. The numbers of sync bytes, gap bytes, lentgh of checksum and so on differs from controller to controller. At least this was not known in good old times. Today, yes, there is a tool to analize this and even raw copy such harddisks. (I bookmarked this website for such purposes, but at the moment when opening it , it keeps blank https://www.drem.info/ )

Yes, some harddisks mentions that on the print. But you have no chance to enter this into the lowlevel format tool of your controller, also those for Atari harddisks do not offer it, even not such specialists like the Scheibenkleister driver. Harddisk formaters always only asks about cylinder and head. Also on MFM/RLL controllers for PC.

They always block the whole track on that head.
Power without the Price. It's not a bug. It's a feature. _/|\_ATARI

1040STFM in PC-Tower (PAK68/2, OvrScn, 4 MB, 1GB SCSI, CD-ROM...) * 2x Falcon 030 32GB/14MB+ScrnBlstrIII * 2x TT030 73GB/20MB+Nova * 520/1040STFM * 520/1040STE * 260/520ST/+ * some Mega ST * 2x Mega STE 500MB/4MB+M.CoCo * Stacy * STBook * SLM605 * SLM804 * SLM605 * SMM804 * SH 204/205 * Megafile 30/44/60 * SF314 * SF354 * 5x Pofo * PC3

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Re: MEGAFILE 60 disk capacity issue

Postby 1st1 » Fri Dec 29, 2017 11:08 pm

ijor wrote:I would recreate the bad sector list if you perform a low level format anyway. May be just run some software that performs a surface test and marks the bad clusters at the high level format.


This is the best way. Because different controllers have different behaviours, some still can handle tracks/sectors which were detected defective by another controller type. I remember some drives which I have, whoch had a quite long defect list, but with the Megafile, with surface test after lowlevel format, they did not show any errors. And on the other side, new errors can be there since the manufacturing scan.
Power without the Price. It's not a bug. It's a feature. _/|\_ATARI

1040STFM in PC-Tower (PAK68/2, OvrScn, 4 MB, 1GB SCSI, CD-ROM...) * 2x Falcon 030 32GB/14MB+ScrnBlstrIII * 2x TT030 73GB/20MB+Nova * 520/1040STFM * 520/1040STE * 260/520ST/+ * some Mega ST * 2x Mega STE 500MB/4MB+M.CoCo * Stacy * STBook * SLM605 * SLM804 * SLM605 * SMM804 * SH 204/205 * Megafile 30/44/60 * SF314 * SF354 * 5x Pofo * PC3

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Re: MEGAFILE 60 disk capacity issue

Postby tzok » Sat Dec 30, 2017 9:05 pm

Sorry but you're wrong, the low level format utility from ICD allows you to enter BFI (a.k.a. offset) and I'm using this driver...
Image
On the other hand I have no RLL controller for PC, to make any extensive diagnostics of this drive.

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Re: MEGAFILE 60 disk capacity issue

Postby Lando_C » Wed Feb 14, 2018 8:56 pm

ICD pro does a real good job of testing the surface when you use the "markbad" option. On both my megafile 20 and 30 that test included the printed list on the drives and some more(new) errors, with ICD pro there is no need to type in the defect list by hand, just run through all the included tests and you'll be fine. One thing: when you format MFM and RLL drives, be sure to have them up to running temperature, becuse a cold formatted drive can stop working en it's hot, and vice versa. It is very tempting to turn down or silence the fan in the megafile case (it is often real loud), but don't do that, the disk is dependent on steady temperature. For this reason also, you should avoid writing to a cold disk right after booting up the machine, wait a few minutes so it warms up or you can literally end up with a file that only reads with a cold drive.
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