[OmniOS-discuss] write amplification zvol

Mon Oct 2 07:51:06 UTC 2017

Hi,

i have tried with a pool with ashift=9 and there is no write amplification,
problem is solved.

But i can't used a ashift=9 with ssd (850 evo), i have read many articles
indicated problems with ashift=9 on ssd.

How ca i do ? does i need to tweak specific zfs value ?

Thanks,

Anthony

2017-09-28 11:48 GMT+02:00 anthony omnios <icoomnios at gmail.com>:

> Thanks for you help Stephan.
>
> i have tried differents LUN with default of 512b and 4096:
>
> LU Name: 600144F04D4F0600000059A588910001
>     Operational Status: Online
>     Provider Name     : sbd
>     Alias             : /dev/zvol/rdsk/filervm2/hdd-110002b
>     View Entry Count  : 1
>     Data File         : /dev/zvol/rdsk/filervm2/hdd-110002b
>     Meta File         : not set
>     Size              : 26843545600
>     Block Size        : 4096
>     Management URL    : not set
>     Vendor ID         : SUN
>     Product ID        : COMSTAR
>     Serial Num        : not set
>     Write Protect     : Disabled
>     Writeback Cache   : Disabled
>     Access State      : Active
>
> Problem is the same.
>
> Cheers,
>
> Anthony
>
> 2017-09-28 10:33 GMT+02:00 Stephan Budach <stephan.budach at jvm.de>:
>
>> ----- Ursprüngliche Mail -----
>>
>> > Von: "anthony omnios" <icoomnios at gmail.com>
>> > An: "Richard Elling" <richard.elling at richardelling.com>
>> > CC: omnios-discuss at lists.omniti.com
>> > Gesendet: Donnerstag, 28. September 2017 09:56:42
>> > Betreff: Re: [OmniOS-discuss] write amplification zvol
>>
>> > Thanks Richard for your help.
>>
>> > My problem is that i have a network ISCSI traffic of 2 MB/s, each 5
>> > seconds i need to write on disks 10 MB of network traffic but on
>> > pool filervm2 I am writing much more that, approximatively 60 MB
>> > each 5 seconds. Each ssd of filervm2 is writting 15 MB every 5
>> > second. When i check with smartmootools every ssd is writing
>> > approximatively 250 GB of data each day.
>>
>> > How can i reduce amont of data writting on each ssd ? i have try to
>> > reduce block size of zvol but it change nothing.
>>
>> > Anthony
>>
>> > 2017-09-28 1:29 GMT+02:00 Richard Elling <
>> > richard.elling at richardelling.com > :
>>
>> > > Comment below...
>> >
>>
>> > > > On Sep 27, 2017, at 12:57 AM, anthony omnios <
>> > > > icoomnios at gmail.com
>> > > > > wrote:
>> >
>> > > >
>> >
>> > > > Hi,
>> >
>> > > >
>> >
>> > > > i have a problem, i used many ISCSI zvol (for each vm), network
>> > > > traffic is 2MB/s between kvm host and filer but i write on disks
>> > > > many more than that. I used a pool with separated mirror zil
>> > > > (intel s3710) and 8 ssd samsung 850 evo 1To
>> >
>> > > >
>> >
>> > > > zpool status
>> >
>> > > > pool: filervm2
>> >
>> > > > state: ONLINE
>> >
>> > > > scan: resilvered 406G in 0h22m with 0 errors on Wed Sep 20
>> > > > 15:45:48
>> > > > 2017
>> >
>> > > > config:
>> >
>> > > >
>> >
>> > > > NAME STATE READ WRITE CKSUM
>> >
>> > > > filervm2 ONLINE 0 0 0
>> >
>> > > > mirror-0 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41657AAFd0 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41F85C0Dd0 ONLINE 0 0 0
>> >
>> > > > mirror-2 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CC7105d0 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CC7127d0 ONLINE 0 0 0
>> >
>> > > > mirror-3 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CD7F7Ed0 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CD83FDd0 ONLINE 0 0 0
>> >
>> > > > mirror-4 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CD7F7Ad0 ONLINE 0 0 0
>> >
>> > > > c7t5002538D41CD7F7Dd0 ONLINE 0 0 0
>> >
>> > > > logs
>> >
>> > > > mirror-1 ONLINE 0 0 0
>> >
>> > > > c4t2d0 ONLINE 0 0 0
>> >
>> > > > c4t4d0 ONLINE 0 0 0
>> >
>> > > >
>> >
>> > > > i used correct ashift of 13 for samsung 850 evo
>> >
>> > > > zdb|grep ashift :
>> >
>> > > >
>> >
>> > > > ashift: 13
>> >
>> > > > ashift: 13
>> >
>> > > > ashift: 13
>> >
>> > > > ashift: 13
>> >
>> > > > ashift: 13
>> >
>> > > >
>> >
>> > > > But i write a lot on ssd every 5 seconds (many more than the
>> > > > network traffic of 2 MB/s)
>> >
>> > > >
>> >
>> > > > iostat -xn -d 1 :
>> >
>> > > >
>> >
>> > > > r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
>> >
>> > > > 11.0 3067.5 288.3 153457.4 6.8 0.5 2.2 0.2 5 14 filervm2
>> >
>>
>> > > filervm2 is seeing 3067 writes per second. This is the interface to
>> > > the upper layers.
>> >
>> > > These writes are small.
>> >
>>
>> > > > 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 rpool
>> >
>> > > > 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c4t0d0
>> >
>> > > > 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c4t1d0
>> >
>> > > > 0.0 552.6 0.0 17284.0 0.0 0.1 0.0 0.2 0 8 c4t2d0
>> >
>> > > > 0.0 552.6 0.0 17284.0 0.0 0.1 0.0 0.2 0 8 c4t4d0
>> >
>>
>> > > The log devices are seeing 552 writes per second and since
>> > > sync=standard that
>> >
>> > > means that the upper layers are requesting syncs.
>> >
>>
>> > > > 1.0 233.3 48.1 10051.6 0.0 0.0 0.0 0.1 0 3 c7t5002538D41657AAFd0
>> >
>> > > > 5.0 250.3 144.2 13207.3 0.0 0.0 0.0 0.1 0 3 c7t5002538D41CC7127d0
>> >
>> > > > 2.0 254.3 24.0 13207.3 0.0 0.0 0.0 0.1 0 4 c7t5002538D41CC7105d0
>> >
>> > > > 3.0 235.3 72.1 10051.6 0.0 0.0 0.0 0.1 0 3 c7t5002538D41F85C0Dd0
>> >
>> > > > 0.0 228.3 0.0 16178.7 0.0 0.0 0.0 0.2 0 4 c7t5002538D41CD83FDd0
>> >
>> > > > 0.0 225.3 0.0 16210.7 0.0 0.0 0.0 0.2 0 4 c7t5002538D41CD7F7Ed0
>> >
>> > > > 0.0 282.3 0.0 19991.1 0.0 0.0 0.0 0.2 0 5 c7t5002538D41CD7F7Dd0
>> >
>> > > > 0.0 280.3 0.0 19871.0 0.0 0.0 0.0 0.2 0 5 c7t5002538D41CD7F7Ad0
>> >
>>
>> > > The pool disks see 1989 writes per second total or 994 writes per
>> > > second logically.
>> >
>>
>> > > It seems to me that reducing 3067 requested writes to 994 logical
>> > > writes is the opposite
>> >
>> > > of amplification. What do you expect?
>> >
>> > > -- richard
>> >
>>
>> > > >
>> >
>> > > > I used zvol of 64k, i try with 8k and problem is the same.
>> >
>> > > >
>> >
>> > > > zfs get all filervm2/hdd-110022a :
>> >
>> > > >
>> >
>> > > > NAME PROPERTY VALUE SOURCE
>> >
>> > > > filervm2/hdd-110022a type volume -
>> >
>> > > > filervm2/hdd-110022a creation Tue May 16 10:24 2017 -
>> >
>> > > > filervm2/hdd-110022a used 5.26G -
>> >
>> > > > filervm2/hdd-110022a available 2.90T -
>> >
>> > > > filervm2/hdd-110022a referenced 5.24G -
>> >
>> > > > filervm2/hdd-110022a compressratio 3.99x -
>> >
>> > > > filervm2/hdd-110022a reservation none default
>> >
>> > > > filervm2/hdd-110022a volsize 25G local
>> >
>> > > > filervm2/hdd-110022a volblocksize 64K -
>> >
>> > > > filervm2/hdd-110022a checksum on default
>> >
>> > > > filervm2/hdd-110022a compression lz4 local
>> >
>> > > > filervm2/hdd-110022a readonly off default
>> >
>> > > > filervm2/hdd-110022a copies 1 default
>> >
>> > > > filervm2/hdd-110022a refreservation none default
>> >
>> > > > filervm2/hdd-110022a primarycache all default
>> >
>> > > > filervm2/hdd-110022a secondarycache all default
>> >
>> > > > filervm2/hdd-110022a usedbysnapshots 15.4M -
>> >
>> > > > filervm2/hdd-110022a usedbydataset 5.24G -
>> >
>> > > > filervm2/hdd-110022a usedbychildren 0 -
>> >
>> > > > filervm2/hdd-110022a usedbyrefreservation 0 -
>> >
>> > > > filervm2/hdd-110022a logbias latency default
>> >
>> > > > filervm2/hdd-110022a dedup off default
>> >
>> > > > filervm2/hdd-110022a mlslabel none default
>> >
>> > > > filervm2/hdd-110022a sync standard local
>> >
>> > > > filervm2/hdd-110022a refcompressratio 3.99x -
>> >
>> > > > filervm2/hdd-110022a written 216K -
>> >
>> > > > filervm2/hdd-110022a logicalused 20.9G -
>> >
>> > > > filervm2/hdd-110022a logicalreferenced 20.9G -
>> >
>> > > > filervm2/hdd-110022a snapshot_limit none default
>> >
>> > > > filervm2/hdd-110022a snapshot_count none default
>> >
>> > > > filervm2/hdd-110022a redundant_metadata all default
>> >
>> > > >
>> >
>> > > > Sorry for my bad english.
>> >
>> > > >
>> >
>> > > > What can be the problem ? thanks
>> >
>> > > >
>> >
>> > > > Best regards,
>> >
>> > > >
>> >
>> > > > Anthony
>> >
>>
>> How did you setup your LUNs? Especially, what is the block size for those
>> LUNs. Could it be, that you went with the default of 512b blocks, where the
>> drives do have 4k or even 8k blocks?
>>
>> Cheers,
>> Stephan
>>
>
>
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