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JonK1
2 Iron

Tier usage - SATA tier used when FC tier is not yet full

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We've recently installed a VMAX10k with three tiers (EFD, FC and SATA). FAST Policy is configured as 'free-for-all' with 100%/100%/100% for the three tiers, so the Symm can determine where to place the data.

After we started migrating data to the VMAX we could see the EFD tier fill up; I've adjusted the FASTVP Reserved Space to 2% so that tier is now 98% full. We could also see data come in on the FC tier and on the SATA tier.

Currently the FC tier is 35% full (total capacity 246TB) and the SATA tier is 18% full (total capacity 182TB). Hence, everything located on the SATA tier could easily fit in the FC tier...

I'm used to the VNX systems filling the higher tiers first. A VNX only pushes data to the slower tiers once the faster tiers are full. I would expect the VMAX to do the same, but is this true? Or did we misconfigure something?

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Quincy561
3 Zinc

Re: Tier usage - SATA tier used when FC tier is not yet full

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The VMAX (76 code) will not put idle data on higher tiers, even if there is plenty of available space on them.

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Quincy561
3 Zinc

Re: Tier usage - SATA tier used when FC tier is not yet full

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The VMAX (76 code) will not put idle data on higher tiers, even if there is plenty of available space on them.

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Allen Ward
4 Germanium

Re: Tier usage - SATA tier used when FC tier is not yet full

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FAST works VERY differently on VMAX compared to VNX Jon. With VMAX there is no concept of "FAST first". Every chunk of data is placed exactly where it belongs based on the measured performance demand. This has some advantages and some disadvantages over the VNX. I'm not going to go into a deep dive here on the pros and cons, Suffice it to say for now if your highest tier is filling up then you are definitely pushing enough workload to fill it up. You need to make sure that your second tier isn't bogging things down. If you are experiencing delays in the FC tier then you will have to have the customer bump up capacity in the EFD tier to meet the demand.

I know I don't need to preach to you about the need for a careful analysis of workload before acquiring such and array. This type of situation should highlight that need to those who quote without gathering the required data first 🙂 Unfortunately the ability to thumb your nose at the sales guys who think this doesnt' matter doesn't make the customer happier when they find out they should probably put more money into their shiny new array already.

JonK1
2 Iron

Re: Tier usage - SATA tier used when FC tier is not yet full

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Excellent guys, thanks for the quick responses! We're not experiencing any performance delays: on the contrary, the response times are nice and low! Just wondering why I was seeing so much free space on the FC tier...

Great arrays!

Additional question: is there a way to see how much data FAST VP has queued to move up/down to tiers? I'm wondering if FAST VP has 'caught up' with all the changes in data access patterns. Of course during the initial seeding/migration of the array we just had some write I/O going to it, but now it's in full production mode the reads are coming in and a block might have to move...

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Allen Ward
4 Germanium

Re: Tier usage - SATA tier used when FC tier is not yet full

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My concern was over the EFD tier being full. If it is completely full that would lead me to believe that there are extents that could justify being there but are forced down to FC. It's possible that it is only a very small percentage of what is in FC that wants to be higher. And it is possible that the config of your FC tier is handling those extents just well enough to not slow things down. Just keep an eye on things as any time a tire is completely full it indicates things being forced somewhere that FAST doesn't believe is optimal for them.

I can't remember if you mentioned... are you running fully thin on this array? Are you binding the pools to the FC tier or EFD?

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JonK1
2 Iron

Re: Tier usage - SATA tier used when FC tier is not yet full

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Aah, gotcha! It's a relatively small EFD tier (about 2%) and a massive FC tier (roughly 60-70% of total array capacity). The rest is SATA. So I definitely agree that there will be probably some blocks fighting for a place in EFD. That said, the EFD drives (according to the Unisphere heatmap) are only 20% loaded performance wise...

It's a fully thin array, and I'm binding the LUNs to the FC tier (Allocate according to FAST = Enabled).

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