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elevator question

DISCUSSION Marko Weber|8000 5 participants 9 messages Mar 17, 2014 – Mar 18, 2014

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#0 lore raw

hello list,
in the xfs faq i read elevator=noop is best when using ssd.
i have the gentoo system on a ssd, but the larger data storage partition on softraid with some sata disks. is elevator=noop in this combo still best?

thx for any cunstructive answer

marko

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#1 lore raw
Quoted 10 lines · On Mon, Mar 17, 2014 at 4:35 PM, Marko Weber|8000 <[email protected]> wrote:

hello list,
in the xfs faq i read elevator=noop is best when using ssd.
i have the gentoo system on a ssd, but the larger data storage partition on softraid with some sata disks.
is elevator=noop in this combo still best?

thx for any cunstructive answer

marko

noop and deadline are best for SSDs. deadline is best for spinning disks with XFS, especially in RAID. Stay away from CFQ as it kills parallelism in XFS

Quoted 14 lines

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#2 lore raw

Am 2014-03-17 16:39, schrieb Grozdan:

Quoted 8 lines · On Mon, Mar 17, 2014 at 4:35 PM, Marko Weber|8000 <[email protected]> wrote:
Quoted 7 lines

hello list,
in the xfs faq i read elevator=noop is best when using ssd.
i have the gentoo system on a ssd, but the larger data storage partition on softraid with some sata disks.
is elevator=noop in this combo still best?

Quoted 7 lines
Quoted 3 lines

thx for any cunstructive answer

marko

noop and deadline are best for SSDs. deadline is best for spinning disks with XFS, especially in RAID. Stay away from CFQ as it kills parallelism in XFS

thx grozdan,
but what, if i have mixed setup in a server ssd + sata ??

marko

Quoted 7 lines
Quoted 7 lines

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Quoted 8 lines
Quoted 8 lines

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#3 lore raw

Marko,

I haven't done this myself, so use at your own risk, but from the archlinux wiki, there's an example of using udev to set one scheduler for non-rotational disks and another for rotational, which sounds like a good general solution for what you're looking for here:

https://wiki.archlinux.org/index.php/Solid_State_Drives#Using_udev_for_one_device_or_HDD.2FSSD_mixed_environment

Cheers,
-Shaun

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Marko Weber|8000
Sent: Monday, March 17, 2014 12:26 PM
To: Xfs
Subject: Re: elevator question

Am 2014-03-17 16:39, schrieb Grozdan:

Quoted 9 lines
Quoted 7 lines · On Mon, Mar 17, 2014 at 4:35 PM, Marko Weber|8000 <[email protected]> wrote:

hello list,
in the xfs faq i read elevator=noop is best when using ssd. i have the gentoo system on a ssd, but the larger data storage partition on softraid with some sata disks.
is elevator=noop in this combo still best?

Quoted 7 lines
Quoted 3 lines

thx for any cunstructive answer

marko

noop and deadline are best for SSDs. deadline is best for spinning disks with XFS, especially in RAID. Stay away from CFQ as it kills parallelism in XFS

thx grozdan,
but what, if i have mixed setup in a server ssd + sata ??

marko

Quoted 7 lines
Quoted 7 lines

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Quoted 8 lines
Quoted 8 lines

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#4 lore raw
In reply to Marko Weber|8000

Le Mon, 17 Mar 2014 18:25:32 +0100
Marko Weber|8000 <[email protected]> écrivait:

Quoted 3 lines

thx grozdan,
but what, if i have mixed setup in a server ssd + sata ??

Very easy, you can set the io scheduler for each device separately at will:

echo 'noop' > /sys/block/sda/queue/scheduler
echo 'deadline' > /sys/block/sdb/queue/scheduler

You can put that in some startup script like /etc/rc.local.

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#5 lore raw
In reply to Marko Weber|8000
Quoted 6 lines · On 3/17/2014 10:35 AM, Marko Weber|8000 wrote:

hello list,
in the xfs faq i read elevator=noop is best when using ssd. i have the gentoo system on a ssd, but the larger data storage partition on softraid with some sata disks.
is elevator=noop in this combo still best?

The elevator is per physical device. For SSD use noop. But with your setup is doesn't matter as md/RAID will run at rust speed.

A better solution is to remove the SSD partition from the md/RAID array, reshape/shrink/rebuild the array to make it happy, whatever is necessary after removing the SSD partition.

Now configure the SSD partition as bcache and enable writeback policy. This will increase the performance of the rust array to SSD level for writes, and for reads after frequently accessed data is cached in your SSD.

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#6 lore raw

Le Mon, 17 Mar 2014 17:51:02 -0500 vous écriviez:

Quoted 4 lines

Now configure the SSD partition as bcache and enable writeback policy. This will increase the performance of the rust array to SSD level for writes, and for reads after frequently accessed data is cached in your SSD.

+1 :) you may also try enhanceIO, flashcache...

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#7 lore raw

Hi,

Am 2014-03-18 10:26, schrieb Emmanuel Florac:

Quoted 8 lines

Le Mon, 17 Mar 2014 17:51:02 -0500 vous écriviez:

Quoted 4 lines

Now configure the SSD partition as bcache and enable writeback policy. This will increase the performance of the rust array to SSD level for writes, and for reads after frequently accessed data is cached in your SSD.

+1 :) you may also try enhanceIO, flashcache...

i am barely new to this issue. What would you xfs guys recommend me? i prefer things i can do with kernel, so its dm-cache? bcache?

the raid is an raid5 with 3 disks at moment. xfs filesystem. do i have to format it again and set special things?

i use nobarrier at moment,

any hints or links or guides or even tipps from you directly would be great,

thanks
marko

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#8 lore raw

Le Tue, 18 Mar 2014 11:18:04 +0100
Marko Weber|8000 <[email protected]> écrivait:

Quoted 2 lines

i am barely new to this issue. What would you xfs guys recommend me? i prefer things i can do with kernel, so its dm-cache? bcache?

The easier will be bcache because it comes included with the kernel.

Quoted 2 lines

the raid is an raid5 with 3 disks at moment. xfs filesystem. do i have to format it again and set special things?

No, only the cache itself must be reformatted.

Quoted 1 line

i use nobarrier at moment,

if you're not using a hardware RAID controller with a battery-backed or flash-based cache, it may be risky. Depends mostly on your write activity and power supply stability, though.

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