On Tue, Mar 09, 2004 at 01:02:48AM -0700, Andreas Dilger wrote:
On Mar 09, 2004 15:46 +0800, Isaac Claymore wrote:
I've got a workload that several clients tend to write to separate files under a same dir simultaneously, resulting in heavily fragmented files. And, even worse, those files are rarely read simultaneously, thus read performance degrades quite alot.
I'm wondering whether there's any feature that helps alleviating fragmentation in such workloads. Does writing to different dirs(of a same filesystem) help?
Very much yes. Files allocated from different directories will get blocks from different parts of the filesystem (if available), so they should be less fragmented. In 2.6 there is a heuristic that files opened by different processes allocate from different parts of a group, even within the same directory, but that only really helps if the files themselves aren't too large (i.e. under 8MB or so).
Thanks, I did some test on this last weekend, and here're the results in case someone is interested:
Yes, very interesting. It would be nice if JFS was in this comparison.
Also, the next step is running each filesystem under your workload (Like test 5) and compare the fragmentation and performance over a longer period of time.
Read below for some more comments...
Test environment:
kernel: 2.6.3 with latest reiser4 patches applied. OS: Debian testing/unstable HW: Intel(R) Pentium(R) 4 CPU 1.80GHz, 256M RAM
For each FS configuration, my test went on as: dumping 3 files of 1G each simultaneously, and measure the fragmentation with 'filefrag'.
Each test iteration was done on a freshly formatted filesystem.
Here goes the figures & my evaluations:
1. reiser3, 3 files under a same dir:
sandbox:/mnt/foo [1016]# dd if=/dev/zero of=f0 bs=16M count=64&;dd if=/dev/zero of=f1 bs=16M count=64&;dd if=/dev/zero of=f2 bs=16M count=64&;wait
sandbox:/mnt/foo [1018]# filefrag f0 f1 f2 f0: 470 extents found f1: 461 extents found f2: 470 extents found
My Evaluation: badly fragmented!
2. reiser3, 3 files under 3 different dirs:
sandbox:/mnt [1028]# dd if=/dev/zero of=dir0/foo bs=16M count=64&;dd if=/dev/zero of=dir1/foo bs=16M count=64&;dd if=/dev/zero of=dir2/foo bs=16M count=64&;wait
sandbox:/mnt [1029]# filefrag dir0/foo dir1/foo dir2/foo dir0/foo: 448 extents found dir1/foo: 462 extents found dir2/foo: 443 extents found
My Evaluation: still bad, spreading the files under different dirs did no visible good.
How about with 10 dirs?
3. ext3, 3 files under a same dir:
sandbox:/mnt/foo [1041]# dd if=/dev/zero of=f0 bs=16M count=64&;dd if=/dev/zero of=f1 bs=16M count=64&;dd if=/dev/zero of=f2 bs=16M count=64&;wait
sandbox:/mnt/foo [1044]# filefrag f0 f1 f2 f0: 202 extents found, perfection would be 9 extents f1: 207 extents found, perfection would be 9 extents f2: 208 extents found, perfection would be 9 extents
My Evaluation: much better than reiser3, yet far from perfection.
4. ext3, 3 files under 3 different dirs:
sandbox:/mnt [1054]# dd if=/dev/zero of=dir0/foo bs=16M count=64&;dd
if=/dev/zero of=dir1/foo bs=16M count=64&;dd if=/dev/zero of=dir2/foo bs=16M count=64&;wait
sandbox:/mnt [1056]# sandbox:/mnt [1056]# filefrag dir0/foo dir1/foo dir2/foo dir0/foo: 91 extents found, perfection would be 9 extents dir1/foo: 9 extents found dir2/foo: 95 extents found, perfection would be 9 extents
My Evaluation: spreading the files under different dirs DID help quite alot! but can we get even better result by spread the files more sparsely? (see next test)
5. still ext3, mkdir 10 dirs first, then dumping the files under the 1st, 5th, and 9th dirs:
sandbox:/mnt [1085]# dd if=/dev/zero of=dir0/foo bs=16M count=64&;dd if=/dev/zero of=dir4/foo bs=16M count=64&;dd if=/dev/zero of=dir9/foo bs=16M count=64&;wait
sandbox:/mnt [1086]# filefrag dir{0,4,9}/foo dir0/foo: 11 extents found, perfection would be 9 extents dir4/foo: 11 extents found, perfection would be 9 extents dir9/foo: 10 extents found, perfection would be 9 extents
My Evaluation: almost perfect!
6. XFS, 3 files under a same dir:
sandbox:/mnt/foo [1112]# dd if=/dev/zero of=f0 bs=16M count=64&;dd if=/dev/zero of=f1 bs=16M count=64&;dd if=/dev/zero of=f2 bs=16M count=64&;wait
sandbox:/mnt/foo [1114]# filefrag f0 f1 f2 f0: 25 extents found f1: 11 extents found f2: 20 extents found
My Evaluation: this'd be the BEST result I got, when dumping into a same dir.
7. XFS, dumping into 3 dirs among ten, similar to test 5:
sandbox:/mnt [1127]# dd if=/dev/zero of=dir0/foo bs=16M count=64&;dd if=/dev/zero of=dir4/foo bs=16M count=64&;dd if=/dev/zero of=dir9/foo bs=16M count=64&;wait
sandbox:/mnt [1128]# filefrag dir0/foo dir4/foo dir9/foo dir0/foo: 1 extent found dir4/foo: 1 extent found dir9/foo: 1 extent found
My Evaluation: impressed! cant be any better now.
How about with 3 dirs?
8. Reiser4, 1 dir
sandbox:/mnt/foo [1155]# dd if=/dev/zero of=f0 bs=16M count=64&;dd if=/dev/zero of=f1 bs=16M count=64&;dd if=/dev/zero of=f2 bs=16M count=64&;wait
sandbox:/mnt/foo [1156]# filefrag f0 f1 f2 f0: 45 extents found f1: 6011 extents found f2: 45 extents found
My Evaluation: far better than it's brother reiser3. the 6011 extents of f1 was weird, i'd have done more iterations to get an average, just blame lazy me ;)
9. Reiser4, 3 dirs among 10:
sandbox:/mnt [1165]# dd if=/dev/zero of=dir0/foo bs=16M count=64&;dd if=/dev/zero of=dir4/foo bs=16M count=64&;dd if=/dev/zero of=dir9/foo bs=16M count=64&;wait
sandbox:/mnt [1167]# filefrag dir{0,4,9}/foo dir0/foo: 42 extents found dir4/foo: 50 extents found dir9/foo: 46 extents found
My Evaluation: nice figures, really. and unlike its elder brother, using more dirs DID help.
How about with 3 dirs?
Mike
_______________________________________________ Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
