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01-10-2018

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DS4200 Tiering problems

2018-01-10, 17:53 PM

Hello,

 

we have new storage DS4200 with active automatic Tiering function (2 SSD - Performance, 10 HDD - Standard) connected via FC to Hyper-V cluster.

We have problems with Tiering Affinity, in write/read stress test of storage we see high load of Standard Tier (screens below). On test volume is set Tiering Affinity = Performance.
In Lenovo manual, is about tiering affinity feature written: "Performance—This setting prioritizes volume data to the higher performing tiers. If no space is available, lower performing tier space is used. Performance affinity volume data will swap into higher tiers based upon frequency of access or when space is made available."

 

Tier statistics:

Performance: Total Size=3834.7GB, Alloc Size=1167.3GB, Available Size=2667.3GB, Affinity Size=1899.9GB
Standard: Total Size=8990.5GB, Alloc Size=1863.9GB, Available Size=7126.6GB, Affinity Size=0B

 

So, in performance tier is allocated only 30% of his space. In this state, all data (3TB) could be in performance tier, in our performance volume is used only 900GB, but when we do write/read tests all tiers are used.

 

We need one performance volume where data will be forced to stay there. We tried change no affinity and performance affinity, but looks like that there is no difference.

 

Have somebody experience with tier affinity, how can we solve this problem?
Thank you very much

____

Today write test:

Another tests:

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7 Posts

12-08-2018

RU

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Re: DS4200 Tiering problems

2019-04-22, 13:35 PM

Hello there!

We are experiencing the same issue here. The firmware version is latest - GT265R010-04

Were you able to solve the problem?

 

We contacted IBM support and they replied that it is not possible to influence tiering process, but were unable to clarify how to move the entire volume to performance tire. Their only suggestion was to create a pool on one of the controllers that consists entirely from SSDs. Having only 2 possible pools is a big limitation.

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2 Posts

01-10-2018

CZ

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Re: DS4200 Tiering problems

2019-04-30, 22:00 PM

Hello,

we found out, that often writing to standard tier was not bug, but feature. Because most of tests are using sequential writes and the storage is using standard HDD for sequential writing, because it's fast enough for this type of writes. Many of tests have random writing feature, but these tests can't reproduce normal production usage.

 

We have now one full SSD pool on the first controller. And tiering pool with 2x SSDs (1 DG, RAID 1) and standard HDDs (3 DG, RAID 5) on the second controller. Tiering in production usage works great, SSDs are full of data and overall performance of the tiering pool is almost same as the full SSD pool.

 

We are using older FW GT265R004 for one year without problems.

 

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7 Posts

12-08-2018

RU

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Re: DS4200 Tiering problems

2019-05-06, 7:51 AM

Thanks a lot, DavidR33

We were actually thinking about the same approach since we need to put the storage in production soon. The strange behaviour of tier affinity feature is confusing. Hope Lenovo will improve documentation to clarify how the algorythm works.

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220 Posts

04-20-2015

CA

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Re: DS4200 Tiering problems

2019-05-06, 12:13 PM

@EvgenyM

 

The tier affinity (see below) is very simple and a way to fine tune the tiering function.

In regards to the algorithm, the system moves hot data every 5 seconds.

 

Volume tier affinity feature The volume tier affinity feature enables tuning the tier-migration algorithm for a virtual volume when creating or modifying the volume so that the volume data automatically moves to a specific tier, if possible. If space is not available in a volume's preferred tier, another tier will be used. There are three volume tier affinity settings:

 

• No Affinity—This setting uses the highest available performing tiers first and only uses the Archive tier when space is exhausted in the other tiers. Volume data will swap into higher performing tiers based on frequency of access and tier space availability.

• Archive—This setting prioritizes the volume data to the least performing tier available. Volume data can move to higher performing tiers based on frequency of access and available space in the tiers.

• Performance—This setting prioritizes volume data to the higher performing tiers. If no space is available, lower performing tier space is used. Performance affinity volume data will swap into higher tiers based upon frequency of access or when space is made available. 

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7 Posts

12-08-2018

RU

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Re: DS4200 Tiering problems

2019-05-06, 13:47 PM

Thanks for the reply. This is a quote from the manual if I remember correctly. But this feature doesn't work this way.

If you add both SAS 10K mechanical drives and SAS SSDs into single pool, and then create a Volume with tier affinity - Performance, the space will be allocated on mechanical drives first in standard tire, not in performance tire, no matter how much free space there is in performance tire in this pool.

That's the problem

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220 Posts

04-20-2015

CA

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  • Message 7 of 7

Re: DS4200 Tiering problems

2019-05-06, 14:17 PM

The data won't move until you start using it (read/write) and the algorithm kicks in  and looks at the in/out data and deems it hot, then moves it od the SSD tier (or the fastest tier in the pool).

 

There is no way to force data to the SSD unless that pool is comprised of SSD only drives; the affinity options are fine tuning options (yes, quoted from manual) but at the end of the day, the algorithm will still move the hot data to the fastest tier in that pool.

 

The post before yours actually confirms this.

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