[ceph-users] Journal / WAL drive size?

Rudi Ahlers rudiahlers at gmail.com
Thu Nov 23 13:18:29 PST 2017


Hi Richard,

So do you rely on the CEPH to automatically decide the WAL device's
location and size?

On Thu, Nov 23, 2017 at 4:04 PM, Richard Hesketh <
richard.hesketh at rd.bbc.co.uk> wrote:

> Keep in mind that as yet we don't really have good estimates for how large
> bluestore metadata DBs may become, but it will be somewhat proportional to
> your number of objects. Considering the size of your OSDs, a 15GB block.db
> partition is almost certainly too small. Unless you've got a compelling
> reason not to you should probably partition your SSDs to use all the
> available space. Personally, I manually partition my block.db devices into
> even partitions and then invoke creation with
>
> ceph-disk prepare --bluestore /dev/sdX --block.db /dev/disk/by-partuuid/
> whateveritis
>
> Invoking by UUID is done because if presented an existing partition rather
> than the root block device it will just symlink precisely to the argument
> given, so using /dev/sdXYZ arguments is dangerous as they may not be
> consistent across hardware changes or even just reboots depending on your
> system.
>
> Rich
>
> On 23/11/17 09:53, Caspar Smit wrote:
> > Rudi,
> >
> > First off all do not deploy an OSD specifying the same seperate device
> for DB and WAL:
> >
> > Please read the following why:
> >
> > http://docs.ceph.com/docs/master/rados/configuration/
> bluestore-config-ref/
> >
> >
> > That said you have a fairly large amount of SSD size available so i
> recommend using it as block.db:
> >
> > You can specify a fixed size block.db size in ceph.conf using:
> >
> > [global]
> > bluestore_block_db_size = 16106127360
> >
> > The above is a 15GB block.db size
> >
> > Now when you deploy an OSD with a seperate block.db device the partition
> will be 15GB.
> >
> > The default size is a percentage of the device i believe and not always
> a usable amount.
> >
> > Caspar
> >
> > Met vriendelijke groet,
> >
> > Caspar Smit
> > Systemengineer
> > SuperNAS
> > Dorsvlegelstraat 13
> > 1445 PA Purmerend
> >
> > t: (+31) 299 410 414
> > e: casparsmit at supernas.eu <mailto:casparsmit at supernas.eu>
> > w: www.supernas.eu <http://www.supernas.eu>
> >
> > 2017-11-23 10:27 GMT+01:00 Rudi Ahlers <rudiahlers at gmail.com <mailto:
> rudiahlers at gmail.com>>:
> >
> >     Hi,
> >
> >     Can someone please explain this to me in layman's terms. How big a
> WAL drive do I really need?
> >
> >     I have a 2x 400GB SSD drives used as WAL / DB drive and 4x 8TB HDD's
> used as OSD's. When I look at the drive partitions the DB / WAL partitions
> are only 576Mb & 1GB respectively. This feels a bit small.
> >
> >
> >     root at virt1:~# lsblk
> >     NAME               MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
> >     sda                  8:0    0   7.3T  0 disk
> >     ├─sda1               8:1    0   100M  0 part /var/lib/ceph/osd/ceph-0
> >     └─sda2               8:2    0   7.3T  0 part
> >     sdb                  8:16   0   7.3T  0 disk
> >     ├─sdb1               8:17   0   100M  0 part /var/lib/ceph/osd/ceph-1
> >     └─sdb2               8:18   0   7.3T  0 part
> >     sdc                  8:32   0   7.3T  0 disk
> >     ├─sdc1               8:33   0   100M  0 part /var/lib/ceph/osd/ceph-2
> >     └─sdc2               8:34   0   7.3T  0 part
> >     sdd                  8:48   0   7.3T  0 disk
> >     ├─sdd1               8:49   0   100M  0 part /var/lib/ceph/osd/ceph-3
> >     └─sdd2               8:50   0   7.3T  0 part
> >     sde                  8:64   0 372.6G  0 disk
> >     ├─sde1               8:65   0     1G  0 part
> >     ├─sde2               8:66   0   576M  0 part
> >     ├─sde3               8:67   0     1G  0 part
> >     └─sde4               8:68   0   576M  0 part
> >     sdf                  8:80   0 372.6G  0 disk
> >     ├─sdf1               8:81   0     1G  0 part
> >     ├─sdf2               8:82   0   576M  0 part
> >     ├─sdf3               8:83   0     1G  0 part
> >     └─sdf4               8:84   0   576M  0 part
> >     sdg                  8:96   0   118G  0 disk
> >     ├─sdg1               8:97   0     1M  0 part
> >     ├─sdg2               8:98   0   256M  0 part /boot/efi
> >     └─sdg3               8:99   0 117.8G  0 part
> >       ├─pve-swap       253:0    0     8G  0 lvm  [SWAP]
> >       ├─pve-root       253:1    0  29.3G  0 lvm  /
> >       ├─pve-data_tmeta 253:2    0    68M  0 lvm
> >       │ └─pve-data     253:4    0  65.9G  0 lvm
> >       └─pve-data_tdata 253:3    0  65.9G  0 lvm
> >         └─pve-data     253:4    0  65.9G  0 lvm
> >
> >
> >
> >
> >     --
> >     Kind Regards
> >     Rudi Ahlers
> >     Website: http://www.rudiahlers.co.za
> >
> >     _______________________________________________
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> >     ceph-users at lists.ceph.com <mailto:ceph-users at lists.ceph.com>
> >     http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com <
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com>
> >
> >
> >
> >
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> >
>
>
> --
> Richard Hesketh
> Systems Engineer, Research Platforms
> BBC Research & Development
>
>
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> ceph-users at lists.ceph.com
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>
>


-- 
Kind Regards
Rudi Ahlers
Website: http://www.rudiahlers.co.za
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