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


Zhen, Liang
 

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, …

 

Regards

Liang

 

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

Hi DAOS,

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?

DJ.

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