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Date:      Wed, 27 Nov 2013 10:42:29 +0100
From:      krichy@cflinux.hu
To:        freebsd-scsi@freebsd.org
Subject:   Fwd: ssd for zfs
Message-ID:  <ef7e350c5edc68ba6c0a33a171c62a2a@cflinux.hu>

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Dear SCSI dev team,

I bought an SSD for my ZFS filesystem to use it as a ZIL. I've tested it 
under linux, and found that it can handle around 1400 random 
synchronized write IOPS. Then I placed it into my freebsd 9.2 box, and 
after attaching it as a ZIL, my zpool only performs 100 (!) write iops. 
I've attached it to an AHCI controller and to an LSI 1068 controller, on 
both it behaves the same. So I expect that something in the scsi layer 
is different, FreeBSD is handling this device slower, but actually it 
can handle the 1400 iops as tested under linux.

I've attached the simple script I used to do the benchmark. basically, 
on linux and bsd also I've added the SSD as a LOG device to an existing 
pool, and run the test on a filesystem in that pool.

Please give some advice where to go, how to debug, and how to improve 
FreeBSD's performance with this drive.

The device is:
# camcontrol identify ada3
pass4: <STEC MACH16 M16SD2S-50UI 00000299> ATA-8 SATA 2.x device
pass4: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 512bytes)

protocol              ATA/ATAPI-8 SATA 2.x
device model          STEC MACH16 M16SD2S-50UI
firmware revision     00000299
serial number         STM0001680E8
WWN                   5000a7203006f8e5
media serial number   STEC MACH16 M16SD2S-50UI STM00
cylinders             16383
heads                 15
sectors/track         63
sector size           logical 512, physical 512, offset 0
LBA supported         97696368 sectors
LBA48 supported       97696368 sectors
PIO supported         PIO4
DMA supported         WDMA2 UDMA6
media RPM             non-rotating

Feature                      Support  Enabled   Value           Vendor
read ahead                     yes	yes
write cache                    yes	yes
flush cache                    yes	yes
overlap                        no
Tagged Command Queuing (TCQ)   no	no
Native Command Queuing (NCQ)   yes		32 tags
SMART                          yes	yes
microcode download             yes	yes
security                       yes	no
power management               yes	yes
advanced power management      no	no
automatic acoustic management  no	no
media status notification      no	no
power-up in Standby            yes	no
write-read-verify              no	no
unload                         no	yes
free-fall                      no	no
Data Set Management (DSM/TRIM) yes
DSM - max 512byte blocks       yes              8
DSM - deterministic read       yes              any value
Host Protected Area (HPA)      yes      no      97696368/97696368
HPA - Security                 no

Regards,

Kojedzinszky Richard
From owner-freebsd-scsi@FreeBSD.ORG  Wed Nov 27 14:14:41 2013
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Date: Wed, 27 Nov 2013 15:14:38 +0100
From: krichy@cflinux.hu
To: freebsd-scsi@freebsd.org
Subject: Fwd: Re: ssd for zfs
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-------- Eredeti üzenet --------
Tárgy: Re: ssd for zfs
Dátum: 2013-11-27 14:07
Feladó: Richard Kojedzinszky <krichy@cflinux.hu>
Címzett: Tom Evans <tevans.uk@googlemail.com>
Másolat: FreeBSD FS <freebsd-fs@freebsd.org>

Dear FS devs,

After some investigation, it turned out that when I turn write-cache off 
under linux, the performance drops to 100 on that OS also. But when 
enabled, 1400 IOPS (synchronous) can be achieved. So I would like to see 
the same on FreeBSD as well. Using camcontrol shows that the write cache 
is enabled, but I may assume that something around this is causing the 
performance degradation. But unfortunately I cannot step forward right 
now.

Regards,

Kojedzinszky Richard

On Wed, 27 Nov 2013, Tom Evans wrote:

> On Wed, Nov 27, 2013 at 8:51 AM, Richard Kojedzinszky 
> <krichy@cflinux.hu> wrote:
>> Dear fs developers,
>> 
>> Probably this is not the best list to report my issue, but please 
>> forward it
>> to where it should get.
>> 
>> I bought an SSD for my ZFS filesystem to use it as a ZIL. I've tested 
>> it
>> under linux, and found that it can handle around 1400 random 
>> synchronized
>> write IOPS. Then I placed it into my freebsd 9.2 box, and after 
>> attaching it
>> as a ZIL, my zpool only performs 100 (!) write iops. I've attached it 
>> to an
>> AHCI controller and to an LSI 1068 controller, on both it behaves the 
>> same.
>> So I expect that something in the scsi layer is different, FreeBSD is
>> handling this device slower, but actually it can handle the 1400 iops 
>> as
>> tested under linux.
>> 
>> Please give some advice where to go, how to debug, and how to improve
>> FreeBSD's performance with this drive.
>> 
> 
> The ZIL is only used for synchronous writes. The majority of writes
> are asynchronous, and the ZIL is not used at all. Plus, a ZIL can only
> increase iops by bundling writes - if your underlying pool is write
> saturated already, then a ZIL can't help - any data written to the ZIL
> has to end up on the pool.
> 
> Test the SSD by itself under FreeBSD to rule out FreeBSD not working
> correctly on the SSD (I doubt this though).
> 
> Cheers
> 
> Tom
> 



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