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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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