On Sun, Jul 22, 2012 at 01:39:29PM -0700, Marc MERLIN wrote:
> Result is the same:
> gandalfthegreat:~# hdparm -tT /dev/mapper/ssdcrypt
>
> /dev/mapper/ssdcrypt:
> Timing cached reads: 16614 MB in 2.00 seconds = 8317.50 MB/sec
> Timing buffered disk reads: 68 MB in 3.08 seconds = 22.09 MB/sec
>
> Grumble.
>
> It shouldn't be a hardware problem since I do see 400MB/s before encryption.
Ok, I'm not sure I understand. I mounted /dev/mapper/ssdcrypt (btrfs)
and when going through the filesystem I get much higher speeds than
using dd on the raw block device.
But... when I run
The test below shows that I can access the encrypted SSD 10x faster by talking
to it through a btrfs filesystem than doing a dd read from the device node.
So I suppose I could just ignore the dd device node thing, however not really.
Let's take a directory with some source files inside:
gandalfthegreat:/var/local# find src | wc -l
15261
gandalfthegreat:/var/local# echo 3 > /proc/sys/vm/drop_caches; time du -sh src
514M src
real 0m5.865s
So on an encrypted spinning disk, it takes 6 seconds.
On my SSD in the same machine with the same encryption and the same btrfs filesystem,
I get 5 times slower:
gandalfthegreat:/mnt/btrfs_pool1/var/local# time du -sh src
514M src
real 0m24.937s
Incidently 5x is also the speed difference between my encrypted HD and encrypted SSD
with dd.
Now, why du is 5x slower and dd of a file from the filesystem is 2.5x
faster, I have no idea :-/
See below:
1) drop caches
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# echo 3 > /proc/sys/vm/drop_caches
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# dd if=w2k-s001.vmdk of=/dev/null
2146631680 bytes (2.1 GB) copied, 8.03898 s, 267 MB/s
-> 267MB/s reading from the file through the encrypted filesystem. That's good.
For comparison
gandalfthegreat:/mnt/mnt2# dd if=w2k-s001.vmdk of=/dev/null
2146631680 bytes (2.1 GB) copied, 4.33393 s, 495 MB/s
-> almost 500MB/s reading through another unencrypted filesystem on the same SSD
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# dd if=/dev/mapper/ssdcrypt of=/dev/null bs=1M count=1000
1048576000 bytes (1.0 GB) copied, 45.1234 s, 23.2 MB/s
-> 23MB/s reading from the block device that my FS is mounted from. WTF?
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# echo 3 > /proc/sys/vm/drop_caches; dd if=w2k-s001.vmdk of=test
2146631680 bytes (2.1 GB) copied, 17.9129 s, 120 MB/s
-> 120MB/s copying a file from the SSD to itself. That's not bad.
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# echo 3 > /proc/sys/vm/drop_caches; dd if=test of=/dev/null
2146631680 bytes (2.1 GB) copied, 8.4907 s, 253 MB/s
-> reading the new copied file still shows 253MB/s, good.
gandalfthegreat:/mnt/btrfs_pool1/var/local/VirtualBox VMs/w2k_virtual# dd if=test of=/dev/null
2146631680 bytes (2.1 GB) copied, 2.11001 s, 1.0 GB/s
-> reading without dropping the cache shows 1GB/s
I'm very lost now, any idea what's going on?
Thanks,
Marc
--
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
.... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/
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