Partition Size Limitations

This may have been discussed somewhere but I cannot find a simple answer via search here or at AW. What are the size limitations on FFS partitions. Also what is the size limitation of an amiga dos3 partition (is it 4gb?), I want to set up a share between AOS and Linux on my A1 but I'd rather have something greater than the 3gb I had.

ace

@acefnq

AFAIK the partition size limit for FFS is caused by a fixed number of bitmap blocks. I always thought that there is a 8GB limit for 512 Byte blocks which could be extended by increasing the file system block size.

However, recently I tested the creation of a 33 GB partition with FFS V45 (the one which comes with OS 3.9) and 512 byte blocks. And I could successfully format it. So the 8gb limit seems not to exist.

However, this huge partition with such a small block size needed about 10 seconds to mount on reboot. Increasing the block size to 4096 bytes fixed this.

So with OS 3.9 there seems to be no size limit for FFS partitions. I don't know which limitations the AFFS driver in Linux has, though.

Bye,
Thomas

@thomas

Quote:
If the blocks are stored as uint16 then max blocks are 65536, so that?s 32 Gbytes, when you use block size of 512,
unless it signed int16 then the max blocks are 32768, and max storage capacity is 16 GBytes, when you use blocks size of 512.

How ever the older IDE devices (AmigaOS3.1) uses IO_OFFSETS in bytes, so a 32 bit offset value equals 4Gbytes max, to support more you need NSD64 support found in new SetPatch (OS3.5/OS3.9) or AmigaOS4 A1ide.device, or you can use TD64 standard.

@LiveForIt

Block numbers are always stored in 32 bit integers, either signed or unsigned. That was not what I meant.

I was speaking about the blocks the bitmap is stored in. Bitmap blocks contain one 32bit checksum and the rest of the block is used for the bitmap, so you have 508*8 bits = 4064 bits per block.

I am not sure (and not interested in) how FFS organizes its bitmap. But as I already wrote, it was my (false) impression that it reserves a fixed number of them. So for example if you reseve 4096 bitmap blocks, you can map 4096 * 4064 = 16,646,144 data blocks which represents a little less than 8 GBytes.

But as I already admitted, my assumption was wrong, there is no such limit, at least not for version 45 of FFS.

Bye,
Thomas

@thomas and Liveforit

Thanks I will stick to my old 3gb to be safe but what is the limit for the new FFS under AOS4?

cheers
ace

@acefnq

I used a 12.5G partition to exchange data from my
linux installation and OS4 on my AONE with no problems,
so at least both linux and AOS4 can work with that size,
this with a standard 512 block size.

@pvanni

Thanks.

ace

@acefnq

Quote:

Provided you can find a disk that large, and are willing to go to extremes, the largest disk the FFS on OS4 can theoretically handle is 4,294,967,295 (= maximum number of blocks) times 4,294,967,295 (= maximum block size) bytes in size. That's 18,446,744,065,119,617,025 bytes total. I wouldn't recommend to use 4GByte blocks, though

If you are going to use a single modern hard disk drive, I would not recommend that you go far beyond 8-16 GBytes for an FFS partition, provided you use 8192 byte blocks. FFS becomes pretty inefficient at managing storage media that large very quickly. Beyond the efficiency problem, you are basically free to choose the partition size you prefer. The partition size limits of old no longer apply to the OS4 version of the FFS.