Re: Beginners ceph journal question

[Robert LeBlanc <robert@xxxxxxxxxxxxx>]

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#1 `readlink /var/lib/ceph/osd/-/journal` If it returns nothing then it is a file, if it returns something it is a partition.

#2 It appears that the default of ceph-deploy is to create and use a partition (I don't use ceph-deploy, so I can't be authoritative). This makes sense as there is a lot of overhead in a file system and a file and by using a raw partition, it cuts that all out and gives better performance.

All writes land at the journal first, then are later flushed to the XFS/EXT4 file system. This helps turn random I/O into 'less'-random I/O. You can see big performance gains by locating the journal on a partition of a quality SSD (there are plenty of threads about "quality" SSD).
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Robert LeBlanc

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On Tue, Jun 9, 2015 at 8:35 AM, Vickey Singh <vickey.singh22693@xxxxxxxxx> wrote:

Thanks Michael for your response.

Could you also please help in understanding 

#1  On my ceph cluster , how can i confirm if journal is on block device partition or on file ? 

#2  Is it true that by default ceph-deploy creates journal on dedicated partition and data on another partition if i use the command  ceph-deploy osd create ceph-node1:/dev/sdb

I want to understand the concept of journals creation in Ceph. Hope you will help me.

- vicky

On Tue, Jun 9, 2015 at 5:28 PM, Michael Kuriger <mk7193@xxxxxx> wrote:

You could mount /dev/sdb to a filesystem, such as /ceph-disk, and then do this:

ceph-deploy osd create ceph-node1:/ceph-disk

Your journal would be a file doing it this way.

 

Michael Kuriger Sr. Unix Systems Engineer * mk7193@xxxxxx |( 818-649-7235

From: Vickey Singh <vickey.singh22693@xxxxxxxxx>
Date: Tuesday, June 9, 2015 at 12:21 AM
To: "ceph-users@xxxxxxxxxxxxxx" <ceph-users@xxxxxxxxxxxxxx>
Subject: Beginners ceph journal question

Hello Cephers 

Beginners question on Ceph Journals creation. Need answers from experts.

- Is it true that by default ceph-deploy creates journal on dedicated partition and data on another partition. It does not creates journal on file ??

ceph-deploy osd create ceph-node1:/dev/sdb

This commands is creating

data partition : /dev/sdb2

Journal Partition : /dev/sdb1

In ceph-deploy command i have not specified journal partition but still it creates a journal on sdb1 ? 

- How can i confirm if journal is on block device partition or on file ?

- How can i create journal on a file ? command would be helpful ?

Regards

Vicky

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