DSM-G600, DNS-3xx and NSA-220 Hack Forum

Are the file sizes consistent?

If you transfer a single 2 GB file, you can get 19MB/sec - but if you transfer 200 x 10 MB files, you'll see a significant drop in speed, even though it's the same amount of data.

No - with 4~9GB files, that would not be the cause - however - disk fragmentation could be.

If you have a spare SATA drive, replace one of the drives in the NAS, format the new drive and test.

That's actually a fallacy, and I know that I'll probably get flamed for saying that.

Perhaps a better way to put it is to say that because of the way ext2 reserves space, fragmentation is less likely to be a problem, but, fragmentation can occur and when it does, throughput takes a significant hit.

Perhaps, because of the larger community's position that ext2 file system doesn't really need to be defragmented, the necessary tools to perform the task have been neglected - I believe there used to be a utility called defrag which appears to no longer be available and may never have been compiled for these processors, so the only option would be to copy the files off the disk, format it and copy them back - and if by doing that you see the performance return to what it previously was, then you'll know whether or not fragmentation was indeed the problem.

>That's actually a fallacy, and I know that I'll probably get flamed for saying that.

That's indeed a fallacy, and the following report demystify it:

http://www.heise-online.co.uk/open/Tuni … s/110398/3

The problem gets worse when there is a mix of many large and small files in the filesystem, for exemple when using bittorent clients.
I saw my disk throughput more than halved because of this, until I created a partition only for BT downloads.

The "filefrag" program, when applied to large files, shows you how severely fragmented your files are.
For example, on a file with 840MB and 14264 extents, disk throughput is about 12MB/s, while on a file with 734MB and only 6 extents it is about 24.4 MB/s (as measured by dividing the file lenght by the seconds reported by the command "time dd if=<your_file> of=/dev/null").

The only cure is to backup everything, delete everything from the root directory (or reformat), and restore from the backup.

Joao

Last edited by jcard (2008-12-16 01:59:35)

Hey guys, I haven't yet had time to reformat the 2nd drive but I found out about the read test using hdparm and I'm wondering if someone could comment on them.

root@DNS-321:/# hdparm -tT /dev/sdb2

/dev/sdb2:
Timing buffer-cache reads:   148 MB in 0.51 seconds = 293813 kB/s
Timing buffered disk reads:   66 MB in 3.00 seconds = 22524 kB/s

Are these bad? Good? Decent?

Have you tried any of the suggestions in the thread?  Did any of them work for you?

Aren't there any utilites for defragmenting filesystem in DNS323 indeed ? I have this nasty fragmentation problem too .... I can copy just downloaded content from torrents folder to PC at rate no more than 4 Mb/s .... (I use transmission 1.5 client) But when I have it copied and dump back to same place ... Coping speed become excellent .... well 19 Mb/s and up to 30 with jumbo frames turned on. My method is effective but very time consuming. for instance it takes as much as  7 Hours to "cure" 80 Gb torrent (6h to copy from and one to dump back)
So some utility is a must for the device .... I'm absolutely newbie in linux and started with gusto but now feel some disappointing