On 2011-09-01 12:17, Brian Fallik wrote:
> On Thu, Sep 1, 2011 at 12:06 PM, Jens Axboe <axboe@xxxxxxxxx> wrote:
>> On 2011-09-01 08:18, Brian Fallik wrote:
>>> Perhaps I should describe what I'm seeing. I have two terminals open.
>>> In one, I launch:
>>> $ watch "ls -l foo* | head -n 20"
>>> In the other terminal I kick off fio. fio first spits out the "Laying
>>> out" messages, one per job. Immediately the full 4MB files appear in
>>> the directory listing. *Then* fio starts writing to the files, as
>>> indicated by the fio output. The size of each file never changes
>>> during the test.
>>>
>>> I wasn't expecting the full 4Mb files to be created before the
>>> sequential writes. I expected to not see any files initially, and
>>> then a file for each job growing at a rate of 200Kbs throughout the
>>> test until reaching the 4MB limit.
>>>
>>> Perhaps I'm just configuring fio incorrectly?
>>
>> That you see them there does not mean they are actually written. Fio
>> will use truncate to setup the files, but only actually fill them with
>> data if you are going to be reading them (or requested overwrite).
>
> Digging deeper, I ran fio under strace:
> 25445 stat("foo0", 0x7ffff0a586b0) = -1 ENOENT (No such file or
> directory)
> 25445 unlink("foo0") = -1 ENOENT (No such file or
> directory)
> 25445 open("foo0", O_WRONLY|O_CREAT, 0644) = 3
> 25445 fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
> 25445 fstatfs(3, {f_type=0x58465342, f_bsize=4096,
> f_blocks=4880335840, f_bfree=4880324644, f_bavail=4880324644,
> f_files=19521474432, f_ffree=19521474273, f_fsid={2065, 0},
> f_namelen=255, f_frsize=4096}) = 0
> 25445 pwrite(3, "\0", 1, 4095) = 1
> 25445 pwrite(3, "\0", 1, 8191) = 1
> ...
> 25445 pwrite(3, "\0", 1, 4194303) = 1
> 25445 fadvise64(3, 0, 4194304, POSIX_FADV_DONTNEED) = 0
> 25445 close(3)
A quick guess would be that your glibc is too old, hence it "emulates"
truncate by helpfully zero filling the file.
--
Jens Axboe
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