Re: [dm-crypt] Problem_wiping

From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] Problem_wiping
Date: Sat, 20 Apr 2019 19:09:23 +0200	[thread overview]
Message-ID: <20190420170923.GA10922@tansi.org> (raw)
In-Reply-To: <35adea23-cf39-664c-d17e-929e42f981b6@comcast.net>

Interesting, I had not noticed. 
You are right though, I get 260MB/s with 5.0.x on hardware 
that used to be about 10x slower for this. This is even a bit 
faster than the ciphers cryptsetup offers.

Indeed time for an update. Should be able to get to it 
some time after Easter.

Thanks!

Arno

On Sat, Apr 20, 2019 at 16:18:50 CEST, Robert Nichols wrote:
> On 4/19/19 8:13 AM, Dernsen wrote:
> >Hi,
> >
> >I prepared a partition on my hdd (no ssd) as described in cryptsetup FAQ (intel i3 3rd gen. ; 4gb ram):
> >
> >Test 1. dd urandom direct on partition:
> >
> >
> >root@pocket-pc:/home/dernsen# dd bs=16M status=progress if=/dev/urandom of=/dev/sda3
> >55566139392 Bytes (56 GB, 52 GiB) kopiert, 1611 s, 34,5 MB/s
> >dd: Fehler beim Schreiben von '/dev/sda3': Auf dem Gerät ist kein Speicherplatz mehr verfügbar
> >3313+0 Datensätze ein
> >3312+0 Datensätze aus
> >55574528000 Bytes (56 GB, 52 GiB) kopiert, 1630,73 s, 34,1 MB/s
> >root@pocket-pc:/home/dernsen#
> >
> >
> >
> >Test 2. dm-crypt + dd on device-mapper:
> >
> >root@pocket-pc:/home/dernsen# cryptsetup open --type plain -d /dev/urandom /dev/sda3 to_be_wiped
> >root@pocket-pc:/home/dernsen# dd bs=16M status=progress if=/dev/zero of=/dev/mapper/to_be_wiped
> >55566139392 Bytes (56 GB, 52 GiB) kopiert, 1536 s, 36,2 MB/s
> >dd: Fehler beim Schreiben von '/dev/mapper/to_be_wiped': Auf dem Gerät ist kein Speicherplatz mehr verfügbar
> >3313+0 Datensätze ein
> >3312+0 Datensätze aus
> >55574528000 Bytes (56 GB, 52 GiB) kopiert, 1554,81 s, 35,7 MB/s
> >root@pocket-pc:/home/dernsen#
> >
> >
> >
> >There is almost no difference in speed.
> >
> >1. Did i do any mistake?
> >2. Is this recommodation still up to date?
> 
> Recent kernels (3.x and newer) have a much faster /dev/urandom, so there is no longer a speedup when overwriting with encrypted zeros. With a 2.6 kernel, I measure just 13 MB/s from /dev/urandom, whereas a 3.10 kernel on the same hardware achieves 251 MB/s from /dev/urandom.
> 
> Perhaps it's time to update the FAQ.
> 
> -- 
> Bob Nichols     "NOSPAM" is really part of my email address.
>                 Do NOT delete it.
> 
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-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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