Partition sizes for Amiga OS 3.1 (SCSI)?

[Thomas]

Partition size limit is a software question.

But you are not asking for partition size limit but for harddrive size limit. Harddrive size limit is 4GB. You can connect a bigger drive if you use only the first 4GB of it. You can use more than 4GB with the right software.

Partitions must not be created outside the harddrive size limit. If you create a partition outside the first 4GB area (or crossing the boundary), writing to this partition will corrupt other partitions sooner or later. It's dangerous to deal with large harddrives.

[Thomas]

Click on Read Configuration, then the values should be right.

Size is calculated as Cylinders * Heads * Blocks per Track * 512
Blocks per Cyl is calculated as Heads * Blocks per Track.

There are only very rare cases where you have to edit the values.

[Thomas]

Please post all values as read by Read Configuration.

If the drive is 4119 MB, it will be shown as 23 MB because everything above 4GB (= 4096 MB) is cut off.

[Thomas]

There is a raw, unformatted size for a drive and after a format lays down the file system there is a much lower size; this is why the Amiga got 880K from a floppy DD, Apple got 800K, and IBM got 720K.

This does not apply to harddrives. They are formatted by the manufacturer and have a fixed number of sectors. All of these sectors are available to the operating system.

[Thomas]

Something I noticed. Here is a picture from the 'net of the same drive (same model #):

http://www.4drives.biz/images/DRIVEPICTURES/IBM_02K3404.jpg

It says 4.51GB USCSI. My drive says 4GB SCSI in the same place. I see more references to this model being 4.5GB than 4GB. I wonder why my drive is labelled as such? Two drives with same model # differing by .5GB seems odd.

My drive came in an SGI O2 and HDToolBox's Read Configuration reports both Seagate and SGI in the text details.

It seems I may have a 4.5xGB drive. Steps, then?

Thanks.



bp

Please post all values as read by Read Configuration. Then I can tell you which values to use to restrict the drive to 4GB. IMHO there is no point to take the hassle with scsi driver patches and third-party file systems just for 0.5 GB.

[Thomas]

"End capacity" might be lower. But your example does not mention end capacity. Your example shows low level format, number of sectors.

File system overhead is another story. For example an empty Amiga floppy formatted with OFS has 837 KB free, not 880K.

For harddrives the low level format is given by the manufacturer and cannot be changed by the operating system. If a harddrive is labelled as 4GB, it has ca. 8,000,000 sectors. This number is fixed for all operating systems.

File system overhead seldomly reduces the formatted capacity by more than 0.1 percent. OFS is a bad example. With FFS for example you get 879KB out of the formatted 880KB. File systems of other operating systems are similar.

[Thomas]

So the type of file system, error correction, sector size, allocation size, file allocation table, all take essentially nothing away from raw storage capacity of the drive?

That's not what I said. They take their needed space when it is needed. But an empty partition is empty. Almost. 0.1 percent of for example 2 GB is 2 MB. Should be enough to store nothing but the volume name and the information that there is nothing.

BTW, you are mixing all up. Error correction is part of the low-level format. It does not account into the 512 bytes user data. Sector size is fixed, I said this already.

If you like pre-allocated storage so much, you can use PFS3. It allocates 20% of the partition from the beginning. On the other hand, it uses the remaining space for data only. All meta-data is stored in the 20%.

This means that on other file systems more space than the file size divided by sectorsize is needed for each file while with PFS3 a file occupies exactly this space only.

[Thomas]

I'm not interested in pre-allocated storage, but how a file system and all of its overhead takes virtually no space.

Like I said, it takes its space when it's needed. For example to store a file of 500 bytes it needs two sectors, not one as you might expect.

[Thomas]

918 * 1 * 9674 * 512 = 4,546,934,784 Bytes

= 4.547 GB = 4.235 GiB = 4.0 GiB + 235 MiB

So everything is right so far.

In order to stay below 4 GiB, just reduce the number of cylinders by 51.

867 * 1 * 9674 * 512 = 4,294,327,296 Bytes = 3.999 GiB.

(2 ^ 32 = 4,294,967,296; that's the magic limit)


Edit: given that the drive is bigger than 4GB and is not yet installed (which means that changing values does not destroy existing data), you could use these completely different values:

Cylinders = 4096
Heads = 1
Blocks per Track = 2048
Blocks per Cyl = 2048

Then you'll get exactly 4 GiB.

[Thomas]

Now that that's sorted, 2GB is the max partition size for AmigaOS 3.1, yes?

AFAIK FFS does not have a partition size limit. But some old programs (including the Commodore Installer) refuse to copy data to a partition which has more than 2 GB of free space. Therefore it is a good idea to limit the partition to 2 GB, then there never can be more than 2 GB free.

I am using HDToolBox. I also have GVP's FaaaaaaastPrep app, can I ignore that in setting this up?

I don't know what Fa...astPrep does. As long as the controller is RDB-compatible, HDToolbox should be fine.