Re: SSD recommendations for OSD journals

["Charles 'Boyo" <charlesboyo@xxxxxxxxx>]

Thank you for the information Mikael.

Counting on the kernel's cache, it appears I will be best served purchasing write-optimized SSDs?

Can you share any information on the SSD you are using, is it PCIe connected?

Another question, since the intention of this storage cluster is relatively cheap storage on commodity hardware, what's the balance between cheap SSDs and reliability since journal failure might result in data loss or will such an event just 'down' the affected OSDs? On a similar note, I am using XFS on the OSDs which also journals, does this affect performance in any way?

Charles

On Sun, Jul 21, 2013 at 9:27 PM, Mikaël Cluseau <mcluseau@xxxxxx> wrote:

Hi,

On 07/22/13 06:05, Charles 'Boyo wrote:

Secondly, I'm unclear about how OSDs use the journal. It appears they write to the journal (in all cases, can't be turned off), ack to the client and then read the journal later to write to backing storage. Is that correct?

Yes

I'm coming from enterprise ZFS with an SSD is also used for write journalling but data flushes are from the disk cache in memory, hence the use of write optimized SSDs. Why can't Ceph be configured to write from RAM instead of reading the journal on flush?

From my stats I can tell that the journal flushes use the kernel's cache and do not hit the SSD. Here, sdd is my journal SSD :

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