MD3 and ME4 tiering and cache

Hello A_Stat,

1. The ME4 is the replacement for the MD3. The MD3 is getting towards the end of it’s offering.
2. There are some small differences in the way that the data is pushed between the tiers dependingu on which method that you are using. Here is the link to the administrator guide which explains a little more about them.  https://topics-cdn.dell.com/pdf/powervault-me4012_administrator-guide_en-us.pdf
3. Tier works based on the types of drives that you have in your system. Here is what we state in the best practice section of the administrator guide on page 185. “In general, it is best to have two tiers instead of three tiers. The highest tier will nearly fill before using the lowest tier. The highest tier must be 95% full before the controller will evict cold pages to a lower tier to make room for incoming writes. Typically, you should use tiers with SSDs and 10K/15K disks, or tiers with SSDs and 7K disks. An exception may be if you need to use both SSDs and faster spinning disks to hit a combination of price for performance, but you cannot hit your capacity needs without the 7K disks; this should be rare.  
4. If you look on page 20 of the Administrator guide it explains about read cache in an ME4.

Please let us know if you have any other questions.

Thank you for your prompt response.

After reading from the admin guide I have some follow up questions

What happened to DDP ? Is it ADAPT now?

So if I wanted to use tiered storage, ssd and 7k, with ADAPT , I would have one pool of 2 groups of 12 disk minimum each , and I would create virtual volumes on that pool?

Would both controllers see the same pool?

Is there any way to control the tiering on the virtual volume level? That is making some volumes benefit more from the ssds and some less?

Hello A_Stat,

1. DDP is used on the MD3’s & ADAPT is used on the ME4.
2. You need a minimum of 1 pool for an ME4. With an MD3 you need a minimum of 1 Virtual Disk, or one DDP.  Here is the link to the MD3 Administrator guide. https://downloads.dell.com/manuals/common/md32xx_md36xx_administrator%20guide_en%20us.pdf
3. In either MD3 or ME4 both controller can see the pools or virtual disk. One controller will own the pool or virtual disk & if that controller fails then the secondary controller will take over access to the pools or virtual disks.
4. If you don’t want to use auto tiering then you can assign pools to specific tiers and it will only write to that tier of disks.

Here are also the links to the support matrix for both an ME4 & MD3.

MD3

https://topics-cdn.dell.com/pdf/powervault-md3200_support-matrix_en-us.pdf

ME4

https://topics-cdn.dell.com/pdf/powervault-me4012_support-matrix_en-us.pdf

Please let us know if you have any other questions.

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1. DDP is used on the MD3’s & ADAPT is used on the ME4.

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I will be using ME4 so no need to refer to MD3 any more

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2. You need a minimum of 1 pool for an ME4. With an MD3 you need a minimum of 1 Virtual Disk, or one DDP.  Here is the link to the MD3 Administrator guide. https://downloads.dell.com/manuals/common/md32xx_md36xx_administrator%20guide_en%20us.pdf

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So to clarify, in order to specify 1 ME4 pool with 2 tiers with ADAPT I need a minimum of 12 HDDs and 12 SSDs?

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4. If you don’t want to use auto tiering then you can assign pools to specific tiers and it will only write to that tier of disks.

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I don’t understand how assigning pools to tiers works. From what I  read in the admin guide, in 1 pool there will be 2 disk groups (in my case), corresponding to 2 different tiers.

Hello A_stat,

The minimum number of drives is dependent on the raid that you will be using. Here is the link to the support matrix & if you look on page 8 it list out of the disk requirements. https://topics-cdn.dell.com/pdf/powervault-me4012_support-matrix_en-us.pdf

If you have 2 different types of drives, then auto tiering is enabled.  You can create 2 pools and have one pool for SSD and one for your spinning drives. You can then create volumes on that pool which will only use the drives that are in that pool. 

Please let us know if you have any other questions.

Hi all, 

sorry for jumping in. but im a bit curious about ME4 tiering. DELL Indonesia technical guy said that ME4 data tiering is on File Level and it's different tiering compared to SC series which run on block level.

this is a bit confusing, because i can't found spesific document that mention how data tiering runs on ME4

I'd be keen to better understand how the tiering works too. The documentation is VERY vague as to how it works, talking about moving "pages" between tiers...

I have to say the admin guide isn't really an admin guide, feels more like a high level feature guide and lacks the right detail.

For me I'd like to know more about how it determines whether data needs to move up or down a tier, and whether this is scheduled or assessing this real-time.

Cheers,

Ben

Hello aloy_si_baik,

With an ME4 tiering is done based on the types of drives that you have in your system.  Tier1= SSD, Tier2= 15k/10k, Tier3= 7.2k.  If you only have a single type of drives, then tiering is not in use.

benloveday, with tiering it moves the data in real time.  When you have different class of drives & data is written, the data will get moved to the correct tier within about 5 seconds.  The tiering is enabled on the system once it is initialized & the first writes of data go to the virtual disks.     

Please let us know if you have any other questions.

Thanks Sam, appreciate the reply.

It would be really great to see this in more detail in the documentation, e.g. some form of architecture picture as well as the timings you mentioned. While it might seem like redundant information, it is very useful as a customer to fully understand how this is working to avoid potential performance issues down the track.

Cheers,

Ben

@DELL-Sam L  

yes i know that data tiering runs on different type of drives and speed. but what i am asking is ME4 use the same method data tiering that runs on Block-level or ME4 runs data tiering only in File-Level? 

as you can see the administrator guide are not giving any detail about how data tiering or ADAPT works. it is only a high level explanation.

So based on the documentation I've seen and playing around with our new ME4, it looks like each 'Page' is a 4MB chunk, so essentially it is 'block' mode.    It moves each 'block' 4MB at a time between the tiers when needed.    You can have data from the same volume spread out over different tiers and your host system won't know the difference or care.

Do i need to set it up for SSDs and HDs in the same pool for tiering to work or can i do a pool of slow and a pool of SSDs?

Thanks

Hello everyone,

"Do i need to set it up for SSDs and HDs in the same pool for tiering to work or can i do a pool of slow and a pool of SSDs?"

Can anybody answer this question?

Thanks

I'm pretty sure that in order to take advantage of the Tiering feature, you would have to have both types of storage in the same pool, as data is only going to be moved around within the same pool.   If you created two separate pools with only each type of storage, Tiering would probably never happen.    You can set an 'affinity' for each Volume you create, so that it will either prefer to stay on 'Performance' (SSD) or 'Archive' (HDD) type storage. (assuming that both types of storage are in the same pool that the Volume is in).   

I'm just an end-user, however, and don't use any Tiering here, but this is what I believe to be the case based on the documentation and looking around within the interface of our ME4.