Re: brtfs on top of dmcrypt with SSD -> ssd or nossd + crypt performance?

[Martin Steigerwald <Martin@lichtvoll.de>]

Hi Marc,

Am Sonntag, 22. Juli 2012 schrieb Marc MERLIN:
> I'm still getting a bit more data before updating the btrfs wiki with
> my best recommendations for today.
> 
> First, everything I've read so far says that the ssd btrfs mount option
> makes btrfs slower in benchmarks.
> What gives?
> Anyone using it or know of a reason not to mount my ssd with nossd?
> 
> 
> Next, I got a new Samsumg 830 512GB SSD which is supposed to be very
> high performance.
> The raw device seems fast enough on a quick hdparm test:
> 
> 
> But once I encrypt it, it drops to 5 times slower than my 1TB spinning
> disk in the same laptop:
> gandalfthegreat:~# hdparm -tT /dev/mapper/ssdcrypt
> /dev/mapper/ssdcrypt:
>  Timing cached reads:   15412 MB in  2.00 seconds = 7715.37 MB/sec
>  Timing buffered disk reads:  70 MB in  3.06 seconds =  22.91 MB/sec
> <<<<
> 
> gandalfthegreat:~# hdparm -tT /dev/mapper/cryptroot (spinning disk)
> /dev/mapper/cryptroot:
>  Timing cached reads:   16222 MB in  2.00 seconds = 8121.03 MB/sec
>  Timing buffered disk reads: 308 MB in  3.01 seconds = 102.24 MB/sec
> <<<<

Have you looked whether certain kernel threads are eating CPU?

I would have a look at this.

Or use atop to have a complete system overview during the hdparm run. You 
may want to use its default 10 seconds delay.

Anyway, hdparm is only a very rough measurement. (Test time 2 / 3 seconds 
is really short.)

Did you repeat tests three or five times and looked at the deviation?

For what it is worth I can beat that with ecryptfs on top of Ext4 ontop of 
an Intel SSD 320 (SATA 300 based):

martin@merkaba:~> su - ms
Passwort: 
ms@merkaba:~> df -hT .
Dateisystem    Typ      Größe Benutzt Verf. Verw% Eingehängt auf
/home/.ms      ecryptfs  224G    211G   11G   96% /home/ms
ms@merkaba:~> dd if=/dev/zero of=testfile bs=1M count=1000 conv=fsync
1000+0 Datensätze ein
1000+0 Datensätze aus
1048576000 Bytes (1,0 GB) kopiert, 20,1466 s, 52,0 MB/s
ms@merkaba:~> rm testfile 
ms@merkaba:~> sudo fstrim /home
[sudo] password for ms: 
ms@merkaba:~>

Thats way slower than a dd without encryption, but its way faster than 
your hdparm figures. The SSD was underutilized according to the harddisk 
LED of this ThinkPad T520 with Intel i5 Sandybridge 2.5 GHz dualcore. Did 
start atop to late to see whats going on.

(I did not yet test ecryptfs on top of BTRFS, but you didn´t test a 
filesystem with hdparm anyway.)

Thanks,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7