Gentoo Archives: gentoo-user

From: Dale <rdalek1967@×××××.com>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] External hard drive and idle activity
Date: Mon, 03 Aug 2020 12:24:36
Message-Id: 6790940e-41d0-0c34-ed92-e8eb2beda996@gmail.com
In Reply to: Re: [gentoo-user] External hard drive and idle activity by Rich Freeman
1 Rich Freeman wrote:
2 > On Mon, Aug 3, 2020 at 1:30 AM Dale <rdalek1967@×××××.com> wrote:
3 >> Little update here. Rich, I think you mentioned it would slow down when it ran out of PMR space while trying to redo the shingled part. Up until now, I hadn't ran into that issue. It seems the PMR section for this drive is somewhere around 40 or 50GBs, maybe 60GBs. I hadn't had time for backups in over a week so it was a good bit larger than usual. It was around 70GBs, maybe 75. When it got close to the end of the rsync process, I noticed it slowed down quite a bit. I'd guess about half or so. Usually it runs at around 180 to 190MBs/sec for larger files. Pretty close to the end, rsync was showing around 100MBs/sec at best. It was a little over on some but mostly a little below that. Earlier in the process, it was the normal speed.
4 > I doubt this particular drop is the result of SMR, assuming 100MB/s is
5 > the instantaneous speed. 100MB/s is still reasonable for a hard drive
6 > - on newer CMR drives I've seen the speed of dd drop from 200MB/s to
7 > 100MB/s for sequential writes as the heads move from one end of the
8 > drive to the other, and then it goes back up to 200MB/s if you start
9 > over at the beginning (badblocks testing and so on).
10 >
11 > That level of drop is probably more likely to be due to filesystem
12 > overhead and so on - fragmentation/etc. When SMR buffer overrun
13 > occurs you REALLY hit a wall and the rates drop quite a bit more than
14 > that. If it were a difference of only 50% most would probably
15 > tolerate it.
16 >
17 > Now, if 100MB/s were an updating average across the entire run then
18 > that would be a different matter, because that would mean that it was
19 > running at 200MB/s for most of the run, and then probably dropping
20 > much closer to 0 for a while so as to drive the overall average down
21 > to 100MB/s. I'm not sure where you're getting those numbers from so I
22 > don't know what period that 100MB/s reflects. For an instantaneous
23 > speed I'd consider it a completely reasonable performance for a
24 > typical hard drive when you're writing to a filesystem. If you were
25 > using dd or maybe copies of very large files on an efficient
26 > filesystem you would get better results.
27 >
28
29
30 I use the --progress option with rsync.  It shows the copy speed,
31 elapsed time etc for each file.  Some files are small and the speed it
32 shows isn't accurate at all because the files are just to tiny to get a
33 accurate measure.  I ignore that info on the smaller files.  Videos
34 however are larger files and sometimes can take a lot longer to copy
35 over.  Those tend to be more accurate.  Anyway, that is where the
36 numbers came from.  I wish I had saved the output but sadly I had
37 finished my OS updates and needed to logout and back in again.
38
39 In the past, I've never seen the drive on the larger files be that slow
40 even toward the end.  Generally, it stays pretty close to 180MBs/sec or
41 so which is what I usually get with PMR drives.  Of course, the PMR
42 drives don't keep doing the bumpy thing for a while when it is done
43 either.  Maybe it is something else but it sure did the bumpy thing a
44 lot longer this time. 
45
46 Either way, just wanted to update that a large copy made it slow down. 
47 Other than the initial copy, this is the largest rsync I've ever done to
48 that drive.  Most are around 20, maybe 25GBs. 
49
50 Dale
51
52 :-)  :-) 

Replies

Subject Author
Re: [gentoo-user] External hard drive and idle activity Rich Freeman <rich0@g.o>