Arch Linux

msw1

Member

Registered: 2014-05-01

Posts: 11

[SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Hello. Today, I ran hdparm -t and noticed unusually low performance:

/dev/sdb:
 Timing buffered disk reads: 342 MB in  3.00 seconds = 113.85 MB/sec

This is on a Samsung 840 EVO with an FX-8320 4.5ghz. Testing /dev/sda, my mechanical hard drive, gives me nearly identical results, which makes pretty much no sense. I ran this about a week ago, and got numbers around 520 MB.
I am using the BFQ scheduler and the Linux-ck kernel. I tried other IO schedulers, but only gotten worsened performance.

The only thing I can think of that I've changed recently was from the performance to ondemand CPU governor. Could that have caused this?

Any help would be appreciated. I am using UEFI/GPT. uname -a:

Linux msw1 3.13.11-2-ck #1 SMP PREEMPT Fri Apr 25 20:19:47 PDT 2014 x86_64 GNU/Linux

EDIT:

Now solved! It turns out the 840 EVO with its TLC NAND is an odd SSD, and that the alignment needs to be a multiple of 1.5.

Last edited by msw1 (2014-05-01 21:28:31)

anatolik

Developer

Registered: 2012-09-27

Posts: 458

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

There are several things that can affect SSD performance and one of the most obvious is disk fragmentation and write amplification.

Start with enabling FSTRIM. Also check arch wiki (and google) they have a bunch of advises about SSD performance https://wiki.archlinux.org/index.php/SS … erformance

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msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

There are several things that can affect SSD performance and one of the most obvious is disk fragmentation and write amplification.

Start with enabling FSTRIM. Also check arch wiki (and google) they have a bunch of advises about SSD performance https://wiki.archlinux.org/index.php/SS … erformance

Thanks for replying.

I was not aware that fragmentation existed with SSDs and ext4.

I have followed that guide. blockdev --getalignoff /dev/sdb returns 0. I have discard set in my fstab. I have also tried running fstrim -v / and fstrim -v /home before running hdparm -t, to no avail.

Last edited by msw1 (2014-05-01 17:42:30)

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

It seems to get worse and worse as the computer runs. Upon the start of the computer, it is at around 200MB, which is still much too slow. Now, hdparm -t gives me:

/dev/sdb:
 Timing buffered disk reads: 272 MB in  3.02 seconds =  90.19 MB/sec

supermariolinux

Member

Registered: 2014-01-21

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I have the same SSD(840 EVO) as you do and i am getting similar results with hdparm -t, although i thought this had something to do with the fact that my SSD is only connected to SATA 2.

Partitions are aligned and manually trimming the partition doesn't seem to change anything.

I noticed there is  new firmware update available on Samsung's website(You can boot from a CD with the ISO without having to use Windows), unfortunately i cannot get it to work as the program just crashes.

Using the standard 3.14.1-1 x86-64 kernel with default cfq scheduler

EDIT: It appears i already have the latest firmware installed, still i recommend checking with

hdparm -i /dev/sdX | grep FwRev

and seeing if new firmware is availbe here: http://www.samsung.com/global/business/ … oads.html#

hparm -t results:

/dev/sdc:
 Timing buffered disk reads: 368 MB in  3.01 seconds = 122.36 MB/sec

Last edited by supermariolinux (2014-05-01 20:14:58)

Name Taken

Banned

Registered: 2014-04-09

Posts: 113

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Everything seems normal for me using 3.10 LTS kernel and 840 PRO SSD.

/dev/sda:
 Timing buffered disk reads: 1506 MB in  3.00 seconds = 501.56 MB/sec

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I had exactly the same issue with my EVO when it was not aligned to EBS. It's 1536 KiB or 2048 KiB (depending of source), so it's safe to set the sector alignment value to 12288 (6144 KiB), multiple of 1536 KiB and 2048 KiB.

Last edited by gedgon (2014-05-01 20:15:21)

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I have the same SSD(840 EVO) as you do and i am getting similar results with hdparm -t, although i thought this had something to do with the fact that my SSD is only connected to SATA 2.

Partitions are aligned and manually trimming the partition doesn't seem to change anything.

I noticed there is  new firmware update available on Samsung's website(You can boot from a CD with the ISO without having to use Windows), unfortunately i cannot get it to work as the program just crashes.

Using the standard 3.14.1-1 x86-64 kernel with default cfq scheduler

EDIT: It appears i already have the latest firmware installed, still i recommend checking with

hdparm -i /dev/sdX | grep FwRev

and seeing if new firmware is availbe here: http://www.samsung.com/global/business/ … oads.html#

hparm -t results:

/dev/sdc:
 Timing buffered disk reads: 368 MB in  3.01 seconds = 122.36 MB/sec

I do have the latest firmware. As for you, it could be SATA2. I, however, have this connected to a SATA3 controller. As I said, this used to get 500+ easily. Now, it's more like 80.

I had exactly the same issue with my EVO when it was not aligned to EBS. It's 1536 KiB or 2048 KiB (depending of source), so it's safe to set the sector alignment value to 12288 (6144 KiB), multiple of 1536 KiB and 2048 KiB.

I wish this solved it. However, I still get the same result:

sudo blockdev --getalignoff /dev/sdb
0

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I wish this solved it. However, I still get the same result:

Unfortunately, to change partitions alignment, you need to repartition your SSD.

Edit: Please post

sudo fdisk -l /dev/sdX

Where X is your SSD

Last edited by gedgon (2014-05-01 20:42:51)

supermariolinux

Member

Registered: 2014-01-21

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

i noticed that both

cat /sys/block/sdc/queue/physical_block_size

cat /sys/block/sdc/queue/logical_block_size

report 512, now i believe this SSD supports advanced format 4096 sectors correct? so i guess its possible my disk is formatted with only 512 byte sectors?
or is this not reporting the correct information? I understand i would need to reformat the drive to change this, so when i do how can i be sure its formatted with 4K sectors?

When i first got ths disk i formatted it with GPT and ext4 partitons using gparted

EDIT: here is what fdisk -l /dev/sdc reports for me:

Disk /dev/sdc: 232.9 GiB, 250059350016 bytes, 488397168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 6B11202A-B789-45D9-AC99-FD39FCCA4F51

Device           Start          End   Size Type
/dev/sdc1         2048         6143     2M BIOS boot partition
/dev/sdc2         6144    209721343   100G Microsoft basic data
/dev/sdc3    209721344    243275775    16G Microsoft basic data
/dev/sdc4    243275776    276830207    16G Microsoft basic data
/dev/sdc5    276830208    488396799 100.9G Microsoft basic data

/dev/sdc2 is my Arch partition, the partiton is listed as a Microsoft basic data type, could this relate to any issues?

Last edited by supermariolinux (2014-05-01 20:52:06)

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I wish this solved it. However, I still get the same result:

Unfortunately, to change partitions alignment, you need to repartition your SSD.

Edit: Please post

sudo fdisk -l /dev/sdX

Where X is your SSD

It gives me this:

Disk /dev/sdb: 232.9 GiB, 250059350016 bytes, 488397168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: E6A55B73-13E3-48E3-92E9-B9D28143D618

Device           Start          End   Size Type
/dev/sdb1         2048       616447   300M Windows recovery environment
/dev/sdb2       616448       821247   100M EFI System
/dev/sdb3       821248      1083391   128M Microsoft reserved
/dev/sdb4      1083392    235458391 111.8G Microsoft basic data
/dev/sdb5    235458560    264755199    14G Linux filesystem
/dev/sdb6    264755200    487411711 106.2G Linux filesystem
/dev/sdb7    487411712    488396799   481M Linux swap

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Yup, it's aligned to 1MiB.

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Yup, it's aligned to 1MiB.

Is that a bad value? If so, how can I fix it?
I partitioned this drive with gparted.

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Is that a bad value? If so, how can I fix it?
I partitioned this drive with gparted.

For example in gdisk http://cillian.wordpress.com/2013/11/16 … -on-linux/ but like I said it's safer to set the sector alignment value to 12288. Of course, remember to make a full backup first. It's fast and easy with Linux partitions https://wiki.archlinux.org/index.php/Rs … tem_backup , not sure about Windows backup these days.

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Is that a bad value? If so, how can I fix it?
I partitioned this drive with gparted.

For example in gdisk http://cillian.wordpress.com/2013/11/16 … -on-linux/ but like I said it's safer to set the sector alignment value to 12288. Of course, remember to make a full backup first. It's fast and easy with Linux partitions https://wiki.archlinux.org/index.php/Rs … tem_backup , not sure about Windows backup these days.

Thank you so much! I used gdisk to align it to 12288, and now I get 500MB/s. I was close to reinstalling Arch. Thanks!

supermariolinux

Member

Registered: 2014-01-21

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Is that a bad value? If so, how can I fix it?
I partitioned this drive with gparted.

For example in gdisk http://cillian.wordpress.com/2013/11/16 … -on-linux/ but like I said it's safer to set the sector alignment value to 12288. Of course, remember to make a full backup first. It's fast and easy with Linux partitions https://wiki.archlinux.org/index.php/Rs … tem_backup , not sure about Windows backup these days.

Thank you so much! I used gdisk to align it to 12288, and now I get 500MB/s. I was close to reinstalling Arch. Thanks!

Did you need to reformat your disk before doing so?

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

For example in gdisk http://cillian.wordpress.com/2013/11/16 … -on-linux/ but like I said it's safer to set the sector alignment value to 12288. Of course, remember to make a full backup first. It's fast and easy with Linux partitions https://wiki.archlinux.org/index.php/Rs … tem_backup , not sure about Windows backup these days.

Thank you so much! I used gdisk to align it to 12288, and now I get 500MB/s. I was close to reinstalling Arch. Thanks!

Did you need to reformat your disk before doing so?

Nope. I didn't have to do anything really. Gdisk remade my GPT, I rebooted, and it was fixed. No data lost or need to restore from backups or anything.

supermariolinux

Member

Registered: 2014-01-21

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Thank you so much! I used gdisk to align it to 12288, and now I get 500MB/s. I was close to reinstalling Arch. Thanks!

Did you need to reformat your disk before doing so?

Nope. I didn't have to do anything really. Gdisk remade my GPT, I rebooted, and it was fixed. No data lost or need to restore from backups or anything.

Nice, anyway thanks for creating this topic, and thanks to gedgon for posting a solution.

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

Nope. I didn't have to do anything really. Gdisk remade my GPT, I rebooted, and it was fixed. No data lost or need to restore from backups or anything.

Not sure if it's a proper way ;)

supermariolinux

Member

Registered: 2014-01-21

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

hmmm well i tried using gdisk but my speeds remain the same, also fdisk reports the same thing as before.

Here is what i did, i put gdisk in expert mode with X, used the L option to change sector alignment value, and entered 12288 as the value, then i wrote the table to the disk with w and rebooted.
but it doesn't appear like anything changed, so i guess i just need to reformat all my partitions?

I know I'm only on SATA 2 but i believe i should be getting values in the 200MB/sec range (SATA 2 max is 3Gbps = 384MB/sec)

gedgon

Member

From: Poland

Registered: 2011-01-27

Posts: 95

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

[...]but it doesn't appear like anything changed[...]

Because that shouldn't change anything ;) I've no idea what msw1 did :)

msw1

Member

Registered: 2014-05-01

Posts: 11

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

hmmm well i tried using gdisk but my speeds remain the same, also fdisk reports the same thing as before.

Here is what i did, i put gdisk in expert mode with X, used the L option to change sector alignment value, and entered 12288 as the value, then i wrote the table to the disk with w and rebooted.
but it doesn't appear like anything changed, so i guess i just need to reformat all my partitions?

I know I'm only on SATA 2 but i believe i should be getting values in the 200MB/sec range (SATA 2 max is 3Gbps = 384MB/sec)

Well, I did all that, but I also ran n and just did the default to everything.

It said it created a 2MB partition.

I have no idea if that's related, but perhaps that was the solution?

EDIT:

There's a bit more to it than that.

I didn't see gedgon's link at first, and attempted the solution at http://lifehacker.com/5837769/make-sure … erformance

I did the resizing to my first partition along with my Windows partition, but didn't do the step of shrinking the preceding space for my Windows partition. gdisk used the preceding 2MB for whatever it did when I ran n.

I have no idea if the resizing fixed it alone, or if the gdisk was necessary. I guess you'll have to try

Last edited by msw1 (2014-05-02 01:59:57)

WonderWoofy

Member

From: Los Gatos, CA

Registered: 2012-05-19

Posts: 8,414

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I just want to confirm that this actually made a small difference for me.  I didn't really take issue with the speed as it was before, but I came across this thread and figured I would give it a whirl.  I have two 250G Samsung 840's one is an evo and one isn't.  They are set up in a btrfs raid1.  I changed the sector alignment to 6144 since this would work if the TLC were aligned to either 1.5 or 2.0 (as suggest by Rod Smith in this post to the 'ask ubuntu' page). 

Before the change, hdparm was reporting ~400MB/s for both disks.  After the change, they now both report ~500MB/s. 

Interesting...

Stunts

Member

From: Portugal

Registered: 2009-03-28

Posts: 339

Website

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

I would just like to add that updating the firmware on my EVO drive has changed the speed from 188Mb/s to 324Mb/s.
(Thanks for the hints on this)
This is quite the change. It also reduced 4 seconds of my boot time...
However, I'm sure I can achieve better with the correct partition alignment too...
I'll update this post as soon as I have something else to show for.

tano70

Member

Registered: 2014-04-16

Posts: 21

Re: [SOLVED] Poor SSD Performance, Low Buffered Disk Reads

this is mine:

Disk /dev/sda: 167,7 GiB, 180045766656 bytes, 351651888 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: F05ADD2C-50AD-4C11-9978-FE9555ACFEBE

Dispositivo        Start         Fine   Size Tipo
/dev/sda1           2048      2050047  1000M Windows recovery environment
/dev/sda2        2050048      2582527   260M EFI System
/dev/sda3        2582528      2844671   128M Microsoft reserved
/dev/sda4        2844672    136134809  63,6G Microsoft basic data
/dev/sda5      177758208    178475007   350M Windows recovery environment
/dev/sda6      178475008    178679807   100M EFI System
/dev/sda7      178679808    187072511     4G Linux filesystem
/dev/sda8      187072512    229809824  20,4G Microsoft basic data
/dev/sda9      229809825    306777239  36,7G Microsoft basic data
/dev/sda10     306778112    336971775  14,4G Windows recovery environment
/dev/sda11     336971776    351651839     7G Intel Fast Flash
/dev/sda12     136134810    177758207  19,9G Microsoft basic data

Last edited by tano70 (2014-06-28 06:35:07)