block size

[Fransisco Aris]

how to verify and determine block size for single disk of EVA?

regards,

[Uwe Zessin · Accepted solution]

The size of a single data block (a physical disk drive or a virtual disk) is 512 bytes. That is defined by the SCSI protocol.

If you want to know how many _blocks_ a physical disk drive has, you need to check with the Storage System Scripting Utility (SSSU):
EVA> ls disk full
\Disk Groups\Default Disk Group\Disk 001 information:
...
formattedcapacity ..: 286749488

Now, 286749488 blocks * 512 byte/block = 146,815,737,856 bytes

modelnumber ..: BD1465822C

Yes, it is a 146GByte disk drive.

[Fransisco Aris]

great.but where the number "512" came from?
is it possible to set it to another size?
thanks.

[Uwe Zessin]

512 is a nice number (2^9 bytes) for a computer. This goes back to the time when floppy disks were being used. The early ones had 128 bytes per sector, but the overhead per track was quite large. Later, you could format with different sector sizes (128, 256, 512... up to 2048 bytes, if I recall correctly).

Why the hard disk drive vendors have chosen exactly 512, I don't know, sorry.

It is not possible for an end-user to chance the size, because the storage protocols have certain assumptions that the block size is always 512 bytes.

Well, in fact, some disk drives are formatted with 520 byte sectors, but the user can use only 512 bytes - the remaining 8 bytes are used internally by the storage array for additional metadata management or checksums.


Note that the low-level data block size must not be confused with the RAID chunk size.

[Fransisco Aris]

amazed me.thanks bro.

[Uwe Zessin]

You're welcome.
It brought back some nice memories, for example when I wrote my first floppy disk formatter program ;-)

[Fransisco Aris]

Uwe Zessin doing magic with his answers :).
thanks for your kindness.