[Haifux] Whole disk encryption, because it costs nothing?

[Eli Billauer]

Etzion Bar-Noy wrote:

> Sequential IO is very simple, relatively, so that you will hardly feel 
> the performance impact testing it.
> Test random IO loads with small packets (0.5K-4K) and you will 
> probably feel the performance impact there.
>
It crossed my mind that a sequential test was too simplistic. My ideal 
test would be a database server running like crazy on the data, but this 
is not my application anyhow. I agree that I should test the system 
"under load" but I can't really think about a realistic "under load" 
scenario for 4 hyperthreaded CPUs. At least not something that I could 
test without turning it into a project. So I went for the session below.

/usr is unencypted. /secret is encrypted. My home directory sits on a 
740 GB ext4 partition, which has seen some activity. /secret and /fresh 
are 20 GB, and are pretty untouched.

The whole system will be reinstalled pretty soon, so I don't care about 
being root and fooling around. ;)

My finding is that encryption still speeds up writes. This is really 
weird. I swear that /fresh was created a minute before I used it on this 
test, so I suppose it can't be in a better shape. Still, writing to 
/secret is faster. The only thing that was slower was removing a lot of 
files in one go.

It's also interesting to note that writing to my home directory was 
considerably slower. So even if encryption turns out to have some 
impact, other factors (partition size? Fragmentation?) seem to be more 
dominant.

So while I still agree with the concept that encryption must surely slow 
down disk writes, my tests show me the contrary.

Insights, anyone?
    Eli

---------- Session follows ---------------

[root at short eli]# tar -c /usr | { cd /secret/delete-this/ && time tar -x ; }
tar: Removing leading `/' from member names
tar: Removing leading `/' from hard link targets

real    5m12.709s
user    0m2.351s
sys    0m31.486s
[root at short eli]# time rm -rf /secret/delete-this

real    0m13.319s
user    0m0.180s
sys    0m5.154s
[root at short eli]# tar -c /usr | { cd /home/eli/delete-this/ && time tar 
-x ; }
tar: Removing leading `/' from member names
tar: Removing leading `/' from hard link targets

real    7m0.826s
user    0m2.344s
sys    0m32.340s
[root at short eli]# time rm -rf /home/eli/delete-this

real    0m8.195s
user    0m0.196s
sys    0m5.620s
[root at short eli]# tar -c /usr | { cd /fresh/delete-this/ && time tar -x ; }
tar: Removing leading `/' from member names
tar: Removing leading `/' from hard link targets

real    5m42.639s
user    0m2.332s
sys    0m36.879s
[root at short eli]# time rm -rf /fresh/delete-this

real    0m9.612s
user    0m0.203s
sys    0m6.275s

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