Hi Sage,
I am doing changes in Bluestore related to minimum allocation size according to ssd and hdd.
This change involves:
1. There are three min alloc sizes now:
a. min_alloc_size: old one, default changed to 0
b. min_alloc_size_hdd: for rotational media, default 64k
c. min_alloc_size_ssd: for ssd, default 4k.
2. Making changes in BlockDevice to maintain its own min_alloc_size. It allows to maintain different min_alloc_size for different devices.
3. Making changes in allocator(stupid, bitmap) interfaces to take min_alloc_size from the corresponding devices.
I have following questions regarding this parameter and use of it in bluestore:
1. I assume this parameter is transient and does not have effect on different values (say changed from 4k to 64k or vice versa) across reboots or different ceph versions?
Is it ondisk anywhere in metadata or in freelist manager in direct or indirect manner? Because having on disk presence could cause confusions by
having new options when existing users move to build with this change.
2. While figuring out the min_alloc_size for devices, I give preferences to old config parameter so that existing configs
are not changed by this code change. Is this right or this is not required?
-Regards,
Ramesh Chander
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