[rgw] increase the first chunk size

[Ray Lv <raylv@xxxxxxxxxxxxx>]

Hi,

Currently, the first chunk size of a radosgw object is 512KB.

Here is a case that most of data workload gets to radosgw is ~ 4MB. With the current first chunk size, each radosgw object is stripped to two chunks (512K + 3.5M). And we’re using several large disks on each host with 40TB capacity. So there will be 10 millions of files on each host. If the first chunk size is increased to 4MB, the number of files on each host will be reduced by 50%. It will be benifitial to performance of read because of reduced dcache and inode cache footprint in main memory (in other words, increased cache hit ratio).

The questions are:

• What’s the rationale behind for the current first chunk size?
• Are there any side effects if it is increased to 4MB?

Thanks,

Ray

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