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bug#12626: Bug?: dd limited to <2G read size (2G-8K) on 64 bit machine?


From: Linda Walsh
Subject: bug#12626: Bug?: dd limited to <2G read size (2G-8K) on 64 bit machine?
Date: Fri, 12 Oct 2012 08:25:10 -0700
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.8.1.24) Gecko/20100228 Lightning/0.9 Thunderbird/2.0.0.24 Mnenhy/0.7.6.666

It's not 'direct':
Ishtar:dev/shm# dd if=/dev/zero of=4G bs=2G count=2
dd: warning: partial read (2147479552 bytes); suggest iflag=fullblock
0+2 records in
0+2 records out
4294959104 bytes (4.3 GB) copied, 4.29234 s, 1.0 GB/s
Ishtar:dev/shm# dd if=/dev/zero of=4G bs=2G count=2 iflag=fullblock
2+0 records in
2+0 records out
4294967296 bytes (4.3 GB) copied, 5.41603 s, 793 MB/s
---
From /dev/shm (file to file)
Ishtar:dev/shm# dd if=4G of=4Ga bs=2G count=2
dd: warning: partial read (2147479552 bytes); suggest iflag=fullblock
0+2 records in
0+2 records out
4294959104 bytes (4.3 GB) copied, 5.52481 s, 777 MB/s
-----------------


Hey guys, this is still a bug though:

Ishtar:dev/shm# dd if=4G of=4Ga bs=4G count=1
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB) copied, 4.0274 s, 533 MB/s
(note no error message....)




Paul Eggert wrote:
On 10/12/2012 02:14 AM, Pádraig Brady wrote:
if you specify ibs and obs seperately,
then you will get writes of the size you requested at least.

Won't there be similar problems with the write system
call too?  Perhaps not on Linda's system, but on other
systems.  Once the buffer size exceeds 2 GB or so,
things get pretty dicey in the wild, not due to any
problem in dd itself, but due to the kernels or
file systems that dd relies on.


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