How come EXT4 slows my ssd so much?

Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

Is the partition correctly aligned?

tmcca · Tux's lil' helper Joined: 24 May 2019 Posts: 120

I was going to say same thing make sure it is aligned. Also use fstrim instead of discard on root. You can use discard on boot I think that is correct approach.

How did you partition drive? Did you use parted?

mike155 · Posted: Thu May 30, 2019 5:33 pm Post subject:

Is ext4's lazy inode table zeroing still running? See: 'man mkfs.ext4', option 'lazy_itable_init'.

NeddySeagoon · Posted: Thu May 30, 2019 6:23 pm Post subject:

RayDude,

RayDude · Posted: Thu May 30, 2019 8:30 pm Post subject:

Thanks for the quick replies.

I used gparted to partition the disk so the alignment should be correct.

I'll put fstrim on root and see if that makes a difference.

I'll check the lazy itable feature as well.
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NeddySeagoon · Posted: Thu May 30, 2019 8:51 pm Post subject:

RayDude,

fstrim is about erasing used but free space in good time before you want to reuse it.
It will make no difference to the read speed.

Boot from a liveCD and rerun the tests when you are sure the partitions are not in use.
Don't even mount them.
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RayDude · Posted: Thu May 30, 2019 9:42 pm Post subject:

Naib · Posted: Fri May 31, 2019 1:13 pm Post subject:

What is the IO scheduler being used?
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Zucca · Posted: Fri May 31, 2019 4:16 pm Post subject:

If you want to test filesystem performance, then use some other tool, like fio for example.

As Neddy said, hdparm "skips" filesystem. You can test disk performance with hdparm or (apparently) partition performance. As to why the partition performance is that much slower on an SSD, I have no clue. It would make sense if it was HDD you're testing...

Maybe it's about the IO scheduler as Naib was questioning.

I want to see how this ends up...
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Naib · Posted: Fri May 31, 2019 4:20 pm Post subject:

also note that hdparm expects pata/sata type devices, nvme is not that so it might mis-report. nvme-tools provides means to do block reads
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Pearlseattle

Hu · Moderator Joined: 06 Mar 2007 Posts: 21639

That is what NeddySeagoon and Zucca both said, yes. The hdparm tests should be usable even on a device with no filesystem at all.

RayDude: please post the actual alignment so we can review whether the alignment is correct. The smartctl -a output could also be interesting. Hide any identifying data (such as serial numbers). We only need general model information.

RayDude · Posted: Sat Jun 01, 2019 12:42 am Post subject:

Update: I ran hdparm from a system-restore boot flash on an unmounted /dev/nvmen0p4 and got the same results.

Thanks for telling me about fio, I'll try it.

I just checked and my kernel is configured for no IO Scheduler. How is that possible?

There are three choices: MQ deadline, Kyber, and BFQ. Which should I select?

What does it use if none is selected. I seriously wonder how I did this...

Update: none is apparently good for NVME: https://wiki.ubuntu.com/Kernel/Reference/IOSchedulers

Edit: since I'm using a raid6 array, it looks like I should use deadline...
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mike155 · Posted: Sat Jun 01, 2019 12:49 am Post subject:

Pearlseattle · Posted: Sat Jun 01, 2019 9:36 pm Post subject:

RayDude · Posted: Sun Jun 02, 2019 5:03 pm Post subject:

RayDude · Posted: Sun Jun 02, 2019 5:09 pm Post subject:

Here's the partition table, according to parted:

molletts · Tux's lil' helper Joined: 16 Feb 2013 Posts: 119

Anon-E-moose · Posted: Mon Jun 03, 2019 3:59 pm Post subject:

hdparm works on devices, not partitions, and (I don't think) arrays.

if you want file system performance, then something like iozone would be more what you need.

Edit to add: not sure why there's a performance difference in your first post, it should make no difference whether you point to whole device or a partition of it, it still uses the whole device, because it talks to the controller (if I'm not mistaken)

https://ssd.userbenchmark.com/SpeedTest/607339/CT1000P1SSD8

If running on a NVMe/PCIe Gen3 x4 slot then the device is supposed to hit ~2000 for reads and ~1700 for writes.
if it's not a gen3 slot then it will be slower, especially if that slot is shared with other cards, which is common on many motherboards.
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Hu · Moderator Joined: 06 Mar 2007 Posts: 21639

Please post the partition table without rounding. sgdisk --print can do this. The parted output is not clear whether the partitions are aligned to any of the commonly important boundaries.

RayDude · Posted: Sat Jun 08, 2019 3:51 pm Post subject: