dd comand :bs parameter unit

E_BOURSEAU · 08-27-2020, 09:39 AM

Hello
I'm trying to duplicate a whole disk in order to be at ease to run tests. Disk is 18 Gbyte large.
To achieve duplication, I use dd command.

Question is about dd parameter unit.
If I specify bs=512 does it mean it duplicates using block of 512 bytes or 512 K bytes ?

command run :
dd if=dev/rdsk/c0t0d0s2 of=/dev/rdsk/c0t9d0s2 bs=512 conv)noerror,sync

The server is equipped with 512 Mbyte of RAM and BUFSIZE is 1024.

Regards.
EB

rnturn · 08-27-2020, 10:07 AM

Quote:

Originally Posted by E_BOURSEAU

Hello
I'm trying to duplicate a whole disk in order to be at ease to run tests. Disk is 18 Gbyte large.
To achieve duplication, I use dd command.

Question is about dd parameter unit.
If I specify bs=512 does it mean it duplicates using block of 512 bytes or 512 K bytes ?

command run :
dd if=dev/rdsk/c0t0d0s2 of=/dev/rdsk/c0t9d0s2 bs=512 conv)noerror,sync

The server is equipped with 512 Mbyte of RAM and BUFSIZE is 1024.

Regards.
EB

From the dd(1) man page:

Code:

bs=BYTES
              read and write up to BYTES bytes at a time (default: 512); over-
              rides ibs and obs

I'd bump that value to something like 32K or 64K... at least.

HTH...

berndbausch · 08-27-2020, 10:19 AM

Quote:

Originally Posted by E_BOURSEAU

dd if=dev/rdsk/c0t0d0s2 of=/dev/rdsk/c0t9d0s2 bs=512 conv)noerror,sync

Linux systems are unlikely to have raw disk device files though. Reminds me of HP-UX.

rtmistler · 08-27-2020, 10:26 AM

I'd do 2M.

And I do believe the K, M, and G modifiers work fine with this command.

E_BOURSEAU · 08-27-2020, 10:58 AM

Thanks for your reply.
I'm trying different bs values.
EB

verndog · 08-27-2020, 01:46 PM

Your missing the front "/" on dev/rdsk/c0t0d0s2. Not sure if you actually executed it or not.

jefro · 08-27-2020, 03:28 PM

I'd consider a file by file copy. Usually still faster than dd with the best tuning.

There is optimal sizes for drives and there may be some unique choices for various media too.

If some run of dd fails due to damaged areas then consider other tools like dd-rescue or (I forget that other) gdd or something.

rnturn · 08-27-2020, 03:33 PM

Quote:

Originally Posted by berndbausch

Linux systems are unlikely to have raw disk device files though. Reminds me of HP-UX.

I only recall some "Big Iron" UNIXes using them. Tru64 and Solaris had/have raw disk devices, i.e., "/dev/rdisk/dsk0[a-h]" and "/dev/rdsk/...". I can only remember Oracle as being interested in using them---supposedly for performance reasons.

syg00 · 08-28-2020, 12:09 AM

Use whatever is convenient - I happen to use 4M; habit over the years, it has no particular logic behind the choice. Last time I did some tracing, the value has no effect on the actual I/O issued. On my old laptop with 512-sector disk, chains of 32-sector I/O were issued by dd - I didn't look to see what the I/O scheduler did in the way of consolidation of chains given that all the addresses were consecutive.

E_BOURSEAU · 08-28-2020, 04:04 AM

Hello,

dd ends after about 1 or 2 hours of job with no warning.
but destination disk is empty !
I can't post anything today because remote acces is down.
I did't check "/" missing. may be a recopy of what I launched. to be checked.
EB

berndbausch · 08-28-2020, 04:06 AM

Can you share the precise command?

E_BOURSEAU · 08-31-2020, 04:32 AM

Hello,

here is : dd if=/dev/rdsk/c0t0d0s2 of=/dev/rdsk/c0t9d0s2 bs=4096k conv=noerror,sync
it's running. tell you more when achieved.
Regards.

fatmac · 08-31-2020, 04:51 AM

For large transfers with 512MB ram, I'd use bs=300M, this will read & write your disk in 300MB chunks using that much ram for the transfers.
(Your system should work OK with the other 212MB of ram.)

berndbausch · 08-31-2020, 05:28 AM

Quote:

Originally Posted by E_BOURSEAU

Hello,

dd if=/dev/rdsk/c0t0d0s2 of=/dev/rdsk/c0t9d0s2 bs=4096k conv=noerror,sync

Sorry for this question, but is /dev/rdsk/c0t9d0s2 a device file?

If yes, and if the command succeeds successfully, the two disk partitions should have the same content.
How do you check that the destination disk is empty?

E_BOURSEAU · 08-31-2020, 05:39 AM

Quote:

Originally Posted by berndbausch

Sorry for this question, but is /dev/rdsk/c0t9d0s2 a device file?

If yes, and if the command succeeds successfully, the two disk partitions should have the same content.
How do you check that the destination disk is empty?

Sun is equipped with 2 identical disks. 1st one is on slot 0 (c0t0d0) and the 2nd one in slot 2 (c0t9d0).
Slot 0 contains disk I want to duplicate and Slot 2 is destination disk.

dd command end but ls -al command show only 2 directories.

Sur I missed something.

EB