One More External SSD Issue [SOLVED]

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crboone
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One More External SSD Issue [SOLVED]

Post by crboone »

My external SSD is running very slowly:

HP-Pavilion-Mini # hdparm -Tt /dev/sdb

/dev/sdb:
Timing cached reads: 8596 MB in 2.00 seconds = 4300.69 MB/sec
Timing buffered disk reads: 334 MB in 3.01 seconds = 110.85 MB/sec

I've done some research and have aligned and realigned the partitions per gdisk /dev/sdb (set to everything from 1024 to 12288) and has nothing worked. (In fact, it was at ~160 MB/sec so all that did was slow the drive down). I reduced the swappiness to 10.

Are there any other thoughts about why this is so slow? I am running the external SSD on USB 3.0, but I thought it would be a lot faster than this. I do have to say that it boots much much more quickly than it did on a non-SSD external -- it boots very fast and Mint is very responsive. But it's still bothersome that the numbers don't bear that out.

Thanks for any help!
Last edited by crboone on Tue Jun 09, 2015 12:45 am, edited 3 times in total.

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Reorx
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Re: One More External SSD Issue/Question for Newbie

Post by Reorx »

USB 3.0 theoretical throughput is 640 MBps. This short article might give a clue > http://www.pcmag.com/article2/0,2817,2359068,00.asp

Real world USB3 throughputs rarely exceed 150 MBps and are typically ~100 MBps
Last edited by Reorx on Mon Jun 08, 2015 12:33 am, edited 1 time in total.
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crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »


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Reorx
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Re: One More External SSD Issue/Question for Newbie

Post by Reorx »

USB3 = bottleneck (for this situation)
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crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »

Ok thanks. I may install the SSD internally to see if that makes a big difference.

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Reorx
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Re: One More External SSD Issue/Question for Newbie

Post by Reorx »

Post back results - I'd be interested to see the difference... :mrgreen:
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Jeepty
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Re: One More External SSD Issue/Question for Newbie

Post by Jeepty »

If it was once fast, and is now slow, it could be a trim problem. Trim, on an ssd, is a lot like defragmenting a traditional hard drive. On a ssd, like on a tradition hard drive, when files are deleted they are simply marked as available to be written over. My understanding is that with a ssd, when old information is due to be written over, the old info must first be read by your computer, then cleared, then the new items written. This is something that slows the ssd down over time. There is a way to enable auto trim on the ssd. I don't know how to do it. There is also a way to check if trim is enabled. I don't know how to do that either! :oops:

But I do know how to manually perform a trim: :roll:

Code: Select all

sudo fstrim /
paste that into the terminal. It may take ten minutes to run and it will look like nothing is happening, but what is happening is all the old information that is stored in the nano's and marked as ready to be overwritten, are actually being cleared and made like new, virgin nano's. Bringing back the original high speed performance of the ssd.

I hope that helps you.

crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »

Hi Jeepty -- I have TRIM enabled via discard in fstab only. The fstrim would not work with the drive on USB 3.

BUT -- I now have the drive installed, and it did improve the speed. Was still hoping for a little more (maybe now the alignment would help?). Here are the results:

HP-Pavilion-Mini # hdparm -Tt /dev/sda

/dev/sda:
Timing cached reads: 8656 MB in 2.00 seconds = 4330.72 MB/sec
Timing buffered disk reads: 1132 MB in 3.00 seconds = 376.87 MB/sec

crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »

fstrim does appear to be working now as well. I'll post that in my other thread.

crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »

Now that I've performed the fstrim, here are the performance numbers:

HP-Pavilion-Mini # sudo fstrim -v /
/: 197093588992 bytes were trimmed

/dev/sda:
Timing cached reads: 8024 MB in 2.00 seconds = 4013.57 MB/sec
Timing buffered disk reads: 1332 MB in 3.00 seconds = 443.34 MB/sec

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Reorx
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Re: One More External SSD Issue/Question for Newbie

Post by Reorx »

crboone wrote:Now that I've performed the fstrim, here are the performance numbers:

HP-Pavilion-Mini # sudo fstrim -v /
/: 197093588992 bytes were trimmed

/dev/sda:
Timing cached reads: 8024 MB in 2.00 seconds = 4013.57 MB/sec
Timing buffered disk reads: 1332 MB in 3.00 seconds = 443.34 MB/sec
Internal or external?

Edit: I answered my own quesiton (saw your other thread)... makes sense that you see 400+ MBps via internal SATA connection. I've never seen anything over 200 MBps with USB (3.0)... The upper limit of what I have seen in real world use is ~150 MBps across USB3.
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Jeepty
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Re: One More External SSD Issue/Question for Newbie

Post by Jeepty »

Reorx wrote: I've never seen anything over 200 MBps with USB (3.0)... The upper limit of what I have seen in real world use is ~150 MBps across USB3.
,

Noticing that bottleneck was good stuff...

crboone, I'd say you are good to go. Most write speeds that I have noticed tend to be up to 500mb/s.

crboone
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Re: One More External SSD Issue/Question for Newbie

Post by crboone »

I've reinstalled Mint on the internal SSD. I'm still getting ~425 MB/sec. It's slightly slower than my earlier reading but that could be because that was immediately post-fstrim and now I've reinstalled the OS.

I was just curious to see if Mint on SSD would boot quicker than our Windows 8.1 machine with a slow Pentium on a 5400 RPM platter. Guess what? Windows fast-boot (partial hibernation) won to the full desktop. But not by much!

Jeepty
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Post by Jeepty »

Sacrilege! Heresy! Just kidding.

That's not exactly Apple's to Apple's though.

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