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List:       freebsd-stable
Subject:    Re: Sandisk CloudSpeed Gen. II Eco Channel SSD vs ZFS = we're in hell
From:       Steven Hartland <killing () multiplay ! co ! uk>
Date:       2016-11-29 14:50:23
Message-ID: 4a2d4074-3455-5edb-4682-f1d6b82022fa () multiplay ! co ! uk
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On 29/11/2016 12:30, Eugene M. Zheganin wrote:
> Hi.
>
> On 28.11.2016 23:07, Steven Hartland wrote:
>> Check your gstat with -dp so you also see deletes, it may be that your
>> drives have a very slow TRIM.
>>
> Indeed, I see a bunch of delete operations, and when TRIM disabled my
> engineers report that the performance is greatly increasing. Is this it ?
>
Yep sounds like the TRIM on the disk is particularly poor.

You can download, compile and run 
http://blog.multiplay.co.uk/dropzone/freebsd/ioctl-delete.c

You can run with: ioctl-delete <device> <startblock> <blockcount>

This will time and give you performance info with regards to delete 
requests.

It uses raw BIO_DELETE commands to the device so eliminates filesystem 
latency (don't run on a device that's in use).

You'll likely want to put some data on there though as often FW 
eliminates the delete if it will have no effect e.g.
dd if=/dev/random of=<device> bs=1m count=20480

     Regards
     Steve
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