|To:||Eric Sandeen <sandeen@xxxxxxxxxxx>|
|Subject:||Re: XFS Preallocate using ALLOCSP|
|From:||Smit Shah <getsmit@xxxxxxxxx>|
|Date:||Mon, 15 Jun 2009 23:44:32 -0700|
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On Mon, Jun 15, 2009 at 8:34 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
Smit Shah wrote:
Even the man page of fallocate says that it allocates and initializes to zero the disk space allocated but when i saw the code i did found out that it does not zero it out. Hence was a kindof confused. So posix_allocate is similar to ALLOCSP when falloc is not supported by the underlying filesystem that is to ftruncate the file and zero it out. So all of them try to allocate contiguous blocks but the only difference is when we use the fallocate in ext4/xfs it does not zero out the preallocated space. Am i right ?
But when i fallocate in ext4 i can see the write performance improvement but not in xfs and reason i found out in one of your previous comments is because of the unwritten flag set in xfs. So how do we see if the unwritten flag is set or not ? I did use xfs_info but it didnt show any such information.
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