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fistrosan

Member

Registered: 2020-04-01

Posts: 171

[SOLVED] Very slow data rate when copying (backup) into external drive

Hi all,

I am trying to back up my home directory (circa 100 G) into an external Seagate 4TB USB drive. Unfortunately it is taking about 48 hours to do so and when it finishes, the USB drive is so damn hot that umount does not even work or it takes about 20 min to unmount it. This is a data rate of about 1.5 M/s which I am pretty sure is too slow for USB 3.0. Can someone give me some advice as to what could I be doing wrong ?

Here is the outout of dmesg | tail -n 15

http://ix.io/2uC9

It seems that is being detected as as SS USB (i.e. type 3) so I see no reasons why this is happening. Any help would be very much appreciated

Last edited by fistrosan (2020-08-25 09:11:44)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,701

Re: [SOLVED] Very slow data rate when copying (backup) into external drive

When I run your numbers, I get 579 kB/s which is about 4.6Mb/s.  But, that is just the data, there is a fair amount of overhead as well.  Regardless, USB should not be the bottleneck.

What kind of sustained write speeds do you expect?   The link below is from tomshardware.com and shows sustained read and write for many small files to several models of drives.   Yours seems to fall into the middle of this chart  https://cdn.mos.cms.futurecdn.net/FuP4F … HKGsdA.png

Perhaps a different approach.  Do you need access to individual files?   What if you use tar to create an archive on the drive?  you might find your sustained write performance improves as tar was designed for streaming.

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fistrosan

Member

Registered: 2020-04-01

Posts: 171

Re: [SOLVED] Very slow data rate when copying (backup) into external drive

You see, I would understand that if I had many thousands of individual files the data rate would be low. About 60 % of the 100 GB I have are already in the form of a couple of dozen files of 2-3 GB size. This is my work data (large data cubes of fortran binary unformatted data). That is why I am suspicious .. have you seen the output of dmesg ? it is actually complaining about the data rate not being a multiple of 4096 ... (!?)

fistrosan

Member

Registered: 2020-04-01

Posts: 171

Re: [SOLVED] Very slow data rate when copying (backup) into external drive

The problem got itself solved without me really doing anything (at least purposely). I managed to backup my 100 G home directory is just under 30 min. This is much more reasonable.