On Fri, 2010-08-13 at 10:24 +0400, Michael Tokarev wrote:
> So why xfs decided the block size is 4K??
We had a similar problem with direct io here, with 2.6.9; I quote from
the Bugzilla:
"mkfs.xfs has md-specific code (!) that looks at the raid flavour to
figure stripe parameters, alignment requirements, etc.
"Raid flavours 4,5 and 6 force the alignment to be the same as the file system
block size (which is 4096 bytes)."
Here's a program to test the alignment requirements:
----
#include <xfs/libxfs.h>
#include <fcntl.h>
int main(int argc, char* argv[])
{
struct dioattr dio;
int tfd = open((argc == 2) ? argv[1] : "/mnt/disk1", O_RDONLY, 0666);
if (ioctl(tfd, XFS_IOC_DIOINFO, &dio) < 0)
perror("ioctl");
else {
printf("min io size = %d\n", dio.d_miniosz);
printf("max io size = %d\n", dio.d_maxiosz);
printf("align = %d\n", dio.d_mem);
}
close(tfd);
return 0;
}
----
The same disk set returned 'align = 4096' for raid 5, but 'align = 512' for raid 0.
--
Roger
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