Weird behaviour from an external disk
Feb. 16th, 2019 09:52 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
rhialtoRecently I bought a new external disk (for doing backups on). [1]
When I got it I started with zeroing it out completely, as a simple test that it is actually working. This went with a nice speed (something like 60-80 MB/s). This speed is probably limited by the USB connection, not the actual disk speed.
Then I started to make the actual first backup onto it. That went very strangely: at first it too went at decent speed (it doesn't reach peak speeds if you copy small files of course), but at some point, it became slow. As in between 5 and 6 MB/s slow. The speed was very consistent. iostat showed me it was doing 85 or 86 transfers of 64 KB per second... steadily even when writing big files.
So I tried the disk with another computer and a different operating system. Also slow! (albeit about 8 MB/s or so).
We had a second disk of this type at hand that wasn't in use yet. So I tried making the backup on that one. I think I did not zero it out beforehand. Maybe that is important, but it seems the only difference in what I did. This second disk was plenty fast.
So I sent back the first disk, and ordered an identical one from a different shop. With the third disk I did the same things as with the first.... and it too became slow. I think it was later in the backup process, though. And while keeping an eye on the speed, it managed to go fast for 10 seconds or so, while I was watching, and then it became slow again.
This is so weird! I can believe that one disk is broken in some difficult to understand way, but two? The problem can't be the computer or its operating system, since the problem didn't vary with that. So the only thing I can think of is some weird firmware bug in the drive, that for some reason decides to start throttling the write speed...
Weird...
I think I'll have to send this one back too, and order a "desk model" of the same size... I have several of those in different sizes and they are all fine (so far).
[1] It is a Western Digital 4 TB USB-3 2,5" disk. They call it "Elements" and "portable". The model number (from its SMART info) is WDC WD40 NMZW-11GZ6S1. Weirdly it is sold as model WDBU6Y0040BBK-WESN, and that is on the outside of the packaging. This is the case for all 3 of the disks.
When I got it I started with zeroing it out completely, as a simple test that it is actually working. This went with a nice speed (something like 60-80 MB/s). This speed is probably limited by the USB connection, not the actual disk speed.
Then I started to make the actual first backup onto it. That went very strangely: at first it too went at decent speed (it doesn't reach peak speeds if you copy small files of course), but at some point, it became slow. As in between 5 and 6 MB/s slow. The speed was very consistent. iostat showed me it was doing 85 or 86 transfers of 64 KB per second... steadily even when writing big files.
So I tried the disk with another computer and a different operating system. Also slow! (albeit about 8 MB/s or so).
We had a second disk of this type at hand that wasn't in use yet. So I tried making the backup on that one. I think I did not zero it out beforehand. Maybe that is important, but it seems the only difference in what I did. This second disk was plenty fast.
So I sent back the first disk, and ordered an identical one from a different shop. With the third disk I did the same things as with the first.... and it too became slow. I think it was later in the backup process, though. And while keeping an eye on the speed, it managed to go fast for 10 seconds or so, while I was watching, and then it became slow again.
This is so weird! I can believe that one disk is broken in some difficult to understand way, but two? The problem can't be the computer or its operating system, since the problem didn't vary with that. So the only thing I can think of is some weird firmware bug in the drive, that for some reason decides to start throttling the write speed...
Weird...
I think I'll have to send this one back too, and order a "desk model" of the same size... I have several of those in different sizes and they are all fine (so far).
[1] It is a Western Digital 4 TB USB-3 2,5" disk. They call it "Elements" and "portable". The model number (from its SMART info) is WDC WD40 NMZW-11GZ6S1. Weirdly it is sold as model WDBU6Y0040BBK-WESN, and that is on the outside of the packaging. This is the case for all 3 of the disks.