Re: [MooseFS-Users] MooseFS 4.0 and new features

[Marin B. <li...@ol...>]

> Could you please make a real example?
> Let's assume a replica 4, 2 SSD chunkservers, 2 hdd chunkservers
> I would like that ACK is returned to the client after the first 2 SSD
> server has wrote the data while the other 2 (up to a goal of 4) are
> still writing

The MooseFS team detailed this extensively in the storage class manual
(see https://moosefs.com/Content/Downloads/moosefs-storage-classes-manu
al.pdf, especially chapter 4 with common use scenarios).

Let:
  - SSD chunkservers be labeled 'A'
  - HDD chunkservers be labeled 'B'.

You may create the following storage class:

    mfsscadmin create -C2A -K2A,2B tiered4

The class is named 'tiered4'. It stores 2 copies on SSD at chunk
creation (-C2A), and adds 2 more on HDD asynchronously (-K2A,2B).

Then, you need to assign this storage class to a directory with:

    mfssetsclass tiered4 <directory>

Furthermore, you may also configure your clients to prefer SSD
chunkservers for R/W operations by adding the following line to
mfsmount.cfg or passing it as a mount option:

    mfspreflabels=A

This would make you clients prefer SSD copies over HDD ones to retrieve
or modify chunks.

Hope it helps you,

Marin.