[ceph-users] Use SSDs for metadata or for a pool cache?

[Gesiel Galvão Bernardes]

Hello,
I am building a new cluster with 4 hosts, which have the following
configuration:

128Gb RAM
12 HDs SATA 8TB 7.2k rpm
2 SSDs 240Gb
2x10GB Network

I will use the cluster to store RBD images of VMs, I thought to use with 2x
replica, if it does not get too slow.

My question is: Using bluestore (default since Luminous, right?), should I
use the SSDs as a "cache pool" or use the SSDs to store the bluestore
metadata? Or could I use 1 SSD for metadata and another for a "cache pool"?

Thank you in advance for your opinions.

Gesiel

[Marc Roos]

- Everyone here will tell you not to use 2x replica, maybe use some
erasure code if you want to save space.
- I cannot say anything about applying the cache pool, did not use it,
read some things that made me doubt it was useful for us. We decided to
put some vm's on ssd rbd pool. Maybe when starting with ceph keep things
simple, if something goes wrong it is easier to fix.
- just try hdd performance, our linux vm's have no problem with the
hdd's only. Windows vm's have. And remember if you loose the ssd, you
loose all osd connected to it, could be a high impact on a small
cluster.




-----Original Message-----
From: Gesiel Galvão Bernardes [mailto:***@gmail.com]
Sent: zondag 18 november 2018 0:03
To: ceph-***@lists.ceph.com
Subject: [ceph-users] Use SSDs for metadata or for a pool cache?


Hello,
I am building a new cluster with 4 hosts, which have the following
configuration:

128Gb RAM
12 HDs SATA 8TB 7.2k rpm
2 SSDs 240Gb
2x10GB Network

I will use the cluster to store RBD images of VMs, I thought to use with
2x replica, if it does not get too slow.

My question is: Using bluestore (default since Luminous, right?), should
I use the SSDs as a "cache pool" or use the SSDs to store the bluestore
metadata? Or could I use 1 SSD for metadata and another for a "cache
pool"?

Thank you in advance for your opinions.

Gesiel