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Low write performance and high CPU usage 
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Joined: Sun Mar 17, 2013 12:35
Posts: 2
Post Low write performance and high CPU usage
Hi,

When writing to the compressed ntfs-partition of my fedora-17/windows-7 dual-boot ssd-powered laptop, I get horrible performance and high CPU useage:
Quote:
[root@localhost win]# dd if=/dev/sda2 of=testfile bs=1M count=100
104857600 bytes (105 MB) copied, 30.0805 s, 3.5 MB/s


I did some system-wide profiling, and almost all cycles are spent inside ntfs_best_match. I tried to defragment the volume, but it didn't yield any improvements. I am using ntfs3g-2012.1.15 shipped by Fedora 17.

Any ideas how to improve this situation?

Thank you in advance, Clemens


Sun Mar 17, 2013 18:49
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NTFS-3G Lead Developer

Joined: Tue Sep 04, 2007 17:22
Posts: 1286
Post Re: Low write performance and high CPU usage
Hi Clemens,

Quote:
When writing to the compressed ntfs-partition of my fedora-17/windows-7 dual-boot ssd-powered laptop, I get horrible performance and high CPU useage:

I did some system-wide profiling, and almost all cycles are spent inside ntfs_best_match.

This is well-known, and the cycles are spent in a single-line loop which occurs in a dichotomic search of the previously met sequences... This one of the two standard ways used by compressors.
Quote:
I tried to defragment the volume, but it didn't yield any improvements.

This is unrelated to fragmentation.

IMHO compression is most valuable for USB keys (slow and small capacity) and for backups (few accesses and less time critical). Compression is unreasonable on a SSD.
Quote:
Any ideas how to improve this situation?

Restrict compression to data compressible (plain text, executables) and rarely read/written. On ntfs you can activate or deactivate compression per directory.

Regards

Jean-Pierre


Sun Mar 17, 2013 20:33
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Joined: Sun Mar 17, 2013 12:35
Posts: 2
Post Re: Low write performance and high CPU usage
Hi Jean-Pierre,

Thanks for your reply.

Quote:
This is well-known, and the cycles are spent in a single-line loop which occurs in a dichotomic search of the previously met sequences... This one of the two standard ways used by compressors.


But isn't NTFS' LZ77 implementation supposed to be a lightweight compression scheme?
This was on a 3.3ghz sandy bridge dual-core notebook, where even heavy-weight compressors such as XZ/7zip reach higher values.

Regards, Clemens


Tue Mar 19, 2013 15:35
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