Re: Why it takes 6% of SCM to record the metadata?

Lombardi, Johann

For the record, we also have a python script to estimate the amount of SCM vs NVMe required for a given middleware/object distribution. See for more information.





From: <> on behalf of "Zhen, Liang" <liang.zhen@...>
Reply-To: "" <>
Date: Tuesday 26 October 2021 at 09:14
To: "" <>
Subject: Re: [daos] Why it takes 6% of SCM to record the metadata?


Hi DJ,


DAOS is using both SCM and SSD for application dataset,  so the 6% is not just for system metadata of DAOS, it is also for user/application metadata and small data. For example, keys and small values(<4k) of KV store, inode and small files of POSIX container, …





From: <> on behalf of cheneydeng via <cheneydeng@...>
Date: Monday, October 25, 2021 at 3:00 PM
To: <>
Subject: [daos] Why it takes 6% of SCM to record the metadata?


I know daos use the SCM to store metadata, I can't find a wiki to describe the details about what and how we stored in the metadata, I guess there must be something like block locations(mapping LBA to PBA) and allocation bookeepers, but I don't understand why it takes so much space? Typically it only takes 0.1% of the SSD space to record metadata in the normal SSD FTL, what's the difference?

And I'm also wondering if the community has some directions on how to use less SCM?


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