Re: cephfs: bind data pool via file layout

[Webert de Souza Lima <webert.boss@xxxxxxxxx>]

Thanks for clarifying that, Gregory.

As said before, we use the file layout to resolve the difference of workloads in those 2 different directories in cephfs.

Would you recommend using 2 filesystems instead? By doing so, each fs would have it's default data pool accordingly.

Regards,

Webert Lima

DevOps Engineer at MAV Tecnologia

Belo Horizonte - Brasil

IRC NICK - WebertRLZ

On Wed, Jun 13, 2018 at 11:33 AM Gregory Farnum <gfarnum@xxxxxxxxxx> wrote:

The backtrace object Zheng referred to is used only for resolving hard links or in disaster recovery scenarios. If the default data pool isn’t available you would stack up pending RADOS writes inside of your mds but the rest of the system would continue unless you manage to run the mds out of memory.
-Greg

On Wed, Jun 13, 2018 at 9:25 AM Webert de Souza Lima <webert.boss@xxxxxxxxx> wrote:

Thank you Zheng.

Does that mean that, when using such feature, our data integrity relies now on both data pools'  integrity/availability?

We currently use such feature in production for dovecot's index files, so we could store this directory on a pool of SSDs only. The main data pool is made of HDDs and stores the email files themselves.

There ain't too many files created, it's just a few files per email user, and basically one directory per user's mailbox.

Each mailbox has a index file that is updated upon every new email received or moved, deleted, read, etc.

I think in this scenario the overhead may be acceptable for us.

Regards,

Webert Lima

DevOps Engineer at MAV Tecnologia

Belo Horizonte - Brasil

IRC NICK - WebertRLZ

On Wed, Jun 13, 2018 at 9:51 AM Yan, Zheng <ukernel@xxxxxxxxx> wrote:

On Wed, Jun 13, 2018 at 3:34 AM Webert de Souza Lima
<webert.boss@xxxxxxxxx> wrote:
>
> hello,
>
> is there any performance impact on cephfs for using file layouts to bind a specific directory in cephfs to a given pool? Of course, such pool is not the default data pool for this cephfs.
>

For each file, no matter which pool file data are stored,  mds alway
create an object in the default data pool. The object in default data
pool is used for storing backtrace. So files stored in non-default
pool have extra overhead on file creation. For large file, the
overhead can be neglect. But for lots of small files, the overhead may
affect performance.


> Regards,
>
> Webert Lima
> DevOps Engineer at MAV Tecnologia
> Belo Horizonte - Brasil
> IRC NICK - WebertRLZ
> _______________________________________________
> ceph-users mailing list
> ceph-users@xxxxxxxxxxxxxx
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com

_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com

_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com