|To:||Ying-Hung Chen <ying@xxxxxxxxxxxxxx>|
|Subject:||Re: howto preallocate to minimize fragmentation|
|From:||Eric Sandeen <sandeen@xxxxxxx>|
|Date:||Fri, 23 Sep 2005 07:58:09 -0500|
|References:||<43329839.2070005@xxxxxxxxxxxxxx> <4332A22B.6070708@xxxxxxx> <4332BFCC.8050803@xxxxxxxxxxxxxx> <4332C248.70503@xxxxxxx> <4332C636.9070509@xxxxxxxxxxxxxx> <4332CE65.2000500@xxxxxxxxxxxxx> <4332CF04.2060604@xxxxxxxxxxxxxx> <4332D17E.6060608@xxxxxxx> <4333A130.7040709@xxxxxxxxxxxxxx>|
|User-agent:||Mozilla Thunderbird 1.0.6 (Macintosh/20050716)|
Ying-Hung Chen wrote:
when I run the sample code, and created "testfile" [yhchen@fc3 ~]$ ./xfs_fcntl testfile [yhchen@fc3 ~]$ ls -l testfile -rwx------ 1 yhchen yhchen 0 Sep 23 14:17 testfile [yhchen@fc3 ~]$ du testfile 20480 testfile [yhchen@fc3 ~]$ du -h testfile 20M testfile I see the filesize is 0, but du does show 20MB However, when I try to determine the file size via fseek, it returns 0. so, what does this kind of allocation mean? does it really mean that it
run xfs_bmap on the resulting file and you'll see...
so, if I write anything within this 20MB range, it will be writing to the allocated space and hence nofragmentation?
what happens if I go over? my guess is if i go over, xfs allocation algorithm will be and there will be fragamentation?
well it depends on what else is going on; if there is plenty of free space after that 20M, then no. but if you have parallel streams writing, then fragmentation past the amount of space you allocated is likely.
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