Re: Using OS disk (SSD) as journal for OSD

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Hello,

On Sat, 12 Sep 2015 17:11:04 +0200 Stefan Eriksson wrote:

> Hi,
> 
> I'm reading the documentation about creating new OSD's and I'm see:
> 
> "The foregoing example assumes a disk dedicated to one Ceph OSD Daemon,
> and a path to an SSD journal partition. We recommend storing the journal
> on a separate drive to maximize throughput. You may dedicate a single
> drive for the journal too (which may be expensive) or place the journal
> on the same disk as the OSD (not recommended as it impairs performance).
> In the foregoing example we store the journal on a partitioned solid
> state drive." From:
> http://ceph.com/docs/master/rados/deployment/ceph-deploy-osd/
> 
> So I would like to create my journals on the same SSD as I have my OS
> (RAID1). Is this good practise to initiate a new disk with:
>
Which SSDs (model)?
Some SSDs are patently unsuited for OSD journals, while others will have
no issues keeping up with the OS and journal duties.

The sda below suggest that your RAID1 is a HW one?
That's a bad choice on two counts, a HW RAID can't be TRIM'ed last I
checked.
And you would get a lot more performance out of a software RAID1 with
journals on both SSDs. 
A RAID 1 still might be OK if you can/want trade performance for
redundancy. 
 
> ceph-deploy disk zap osdserver1:sdb
> ceph-deploy osd prepare osdserver1:sdb:/dev/sda
> 
I'm not a ceph-deploy expert or fan, but I'm pretty sure you will need to
create the partitions beforehand and then assign them accordingly.
And using uuids makes things renumbering proof:

ceph-deploy osd prepare ceph-04:sdb:/dev/disk/by-id/wwn-0x55cd2e404b73d348-part4

Christian

> parted info on sda is:
> 
> Number  Start   End     Size    File system     Name     Flags
>  1      1049kB  211MB   210MB   ext4                     boot
>  2      211MB   21.2GB  21.0GB  ext4
>  3      21.2GB  29.6GB  8389MB  linux-swap(v1)
> 
> There is enough space for many 5G journal patitions on sda


-- 
Christian Balzer        Network/Systems Engineer                
chibi@xxxxxxx   	Global OnLine Japan/Fusion Communications
http://www.gol.com/
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