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Slow write performance on IBM Serveraid M1015 (Win 7)

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Hi,

since I am using the IBM Serveraid M1015 (2 channel SAS Controller with 8 SATA connections) for quite a while, I started using it in a dual boot configuration with Fedora 21 and Veracrypt of course.

Speeds are quite the same like an non-decrypted system, aproximately 150 MB/s read and 120 MB/s write on a single device.

But it was shocked, after I installed Windows 7 on a non encrypted device and mounted some drives for the slow write performance. Read speeds stayed the same.

So first, I blamed a non working aes-ni for it, but since it was enabled in BIOS and therefore Windows 7, it could note resulte in write speed slow as 20 MB/s.

Second, I was thinking that a used quick format NTFS could result in such slow write speeds, but a normal formatting did not change anything.

Then I attached the single drive to the mainboard's SATA controller and suddenly the performance was the same like in Fedora - full write speed.

Maybe the drivers of the IBM M1015 did not implement well, but I had no difference with non decrypted devices between Windows 7 and Fedora.

I also used Veracrypt container files (encrypted) on an non-encrypted NTFS formatted drive, but got no better write performance.

The only conclusion is, that since the IBM M1015 doesn't have an Cache, so it uses Write-Through, it may result in that slow write performance. But why only with encryption?

And the Mainboard controller doesn't have a Cache too, but performance like it should.

System

Mainboard:ASUS P9D-X (Intel C202 Chipset, Socket 1150)
CPU: Intel Xeon E3-1225 v3, 4x 3.20GHz
RAM: 16 GiB ECC unbuffered
Disks: 7 Western Digital RED 2 TB, 5400 RPM, SATA 600

Write Performance was tested with Explorer (file copy), Teracopy, rsync, ATTO, Diskmark

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