Am Sonntag, 17. Juni 2012 schrieb Geert Uytterhoeven:
On Sun, Jun 17, 2012 at 2:58 PM, Martin Steigerwald
<Martin@xxxxxxxxxxxx> wrote:
Am Sonntag, 17. Juni 2012 schrieb jdow:
| JXFS 64 bit file system
|
| With AmigaOS 4.x a new file system has been introduced called JXFS.
| It is a totally new 64 bit file system that supports partitions up
| to 16 TB in size. It is a modern journalling file system, which
| means that it reduces data loss if data writes to the disk are
| interrupted. It is the fastest and most reliable file system ever
| created for AmigaOS.
http://www.amigaos.net/content/1/features
Well I asked AmigaOS 4 developers about this issue as well. Lets see
what they say about 2 TB limits.
16 TB = 2 TB * 8. Perhaps they increased the block size from 512 to
4096?
block/partitions/amiga.c reads the block size from
RigidDiskBlock.rdb_BlockBytes,
but after conversion to 512-byte blocks, all further calculations are
done on "int", so it will overflow for disks larger than 2 TiB.
Meanwhile I got a response from a AmigaOS 4 developer.
I documented the stuff as I understood it in the AmigaOS wiki:
| Disk size
|
| The RDB has a quite high limit on the maximum device size, but note that
| currently each filesystem interprets the partition layout by itself.
| The raw, theoretical limit on the maximum device capacity is about 2^105
| bytes:
|
| 32 bit rdb_Cylinders * 32 bit rdb_Heads * 32 bit rdb_Sectors * 512
| bytes/sector for the HD size in struct RigidDiskBlock
|
| It's even much more if the sector size (rdb_BlockBytes and de_SizeBlock)
| is larger than 512 bytes, but AmigaOS 4.1 doesn't support anything but
| 512 bytes/sector HDs yet.
|
| Partition size
|
| For the partitions the maximum size is:
| 32 bit (de_HighCyl + 1 - de_LowCyl) (to get the partition size) * 32 bit
| de_Surfaces * 32 bit de_SectorsPerTrack * 512 bytes/sector in struct
| DosEnvec (=pb_Environment[]) in struct PartitionBlock.
|
| That's from the physical drive part, the actual disk size limit for the
| partitions may be much smaller depending on the partitioning software,
| if it's only using the logical sizes instead, which is likely the case,
| it's only 8 ZiB with 512 bytes/sector: 32 bit rdb_HiCylinder * 32 bit
| rdb_CylBlocks * 512 bytes/sector = 2^73 bytes. For using the logical
| sizes using simple uint64 calculations (with some overflow checks) should
| be enough, for more a math library with support for larger integers
| needs to be used which probably no partitioning software does.
|
| But note: Nothing in struct RigiDiskBlock is used by the file systems for
| mounting the partitions, they only get the information from the struct
| PartitionBlock blocks, it's only a problem for the partitioning software
| creating the partitions correctly - as soon as there are HDs larger than
| 8 ZB while still using 512 bytes/sector if that ever happens.
http://wiki.amigaos.net/index.php/RDB
Please note that the documentation there might be updated or corrected in
the future. But thats the current state.
Note that in your profile-binary.img, the field is 0x200, i.e. 512
bytes per block,
so I'll have to get a deeper look into your RDB first...
I am a bit overwhelmed by Joanne´s analysis. I didn´t yet take time to
completely read and try to understand it. I first wanted to get this
information out.
Thanks,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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