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

[Gandalf C. <gan...@gm...>]

Il dom 20 mag 2018, 15:38 Marin Bernard <li...@ol...> ha scritto:

> MooseFS chunkservers have the HDD_FSYNC_BEFORE_CLOSE config setting
> (default off) which does just that. The equivalent setting on LizardFS
> is PERFORM_FSYNC (default on). The performance penalty with
> PERFORM_FSYNC=1 is very high, though.
>
> If you use ZFS as a backend (which I do), fsync may be enforced at the
> file system level, which is probably more efficient as it bypasses the
> kernel buffer cache (ZFS uses its own). Performance penalty is higher
> than on other file systems because in async mode, ZFS batches disk
> transactions to minimize latency -- a performance boost which is lost
> when fsync is enabled. If performance is critical, you may improve it
> with zlogs.
>

No, data reliability and consistancy is more important for us

>
> I think you can do the same in MooseFS with storage classes: just
> specify a different label expression for chunk Creation and Keep steps.
> This way, you may even decide to assign newly created chunks to
> specific chunk servers. With LizardFS, there is no way to limit chunk
> creation to a subset of chunkservers: they are always distributed
> randomly. That's a problem when half of your servers are part of
> another site.
>

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

>