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I have 4 Samsung 840 Pro SSDs running in hardware RAID on an Intel RS2BL080 LSI RAID card. My read and write times are incredible:

$ dd bs=1M count=10000 if=/dev/zero of=test.img conv=fdatasync 
10000+0 records in 
10000+0 records out 10485760000 bytes (10 GB) copied, 6.3633 s, 1.6 GB/s

Read times are at about 2.0GB/s.

However, when I try duplicating a local file, I'll see my write speed drop to around 200MB/s. What could be going wrong here?

Here is my RAID card configuration, perhaps I misconfigured something? Any one of these drives can get >450MB/s write speed, I've seen it before while not using RAID.


Interestingly enough, I've found that some of these limitations have to do with the filesystem. ext4 starts out fast and slows down to a rate of about 230MB/s. btrfs however, only slowed to about 830MB/s. ntfs was slow like ext4. Are there configuration options for ext4 to speed it up?

share|improve this question
What is the mount option for ext4? Maybe post your /etc/fstab. – John Siu Jan 24 '13 at 2:17

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