[ovirt-users] Gluster storage question

Sat Feb 11 19:18:40 UTC 2017

On 11 February 2017 at 15:39, Bartosiak-Jentys, Chris <
chris.bartosiak-jentys at certico.co.uk> wrote:

> Thank you for your reply Doug,
>
> I didn't use localhost as I was preparing to follow instructions (blog
> post: http://community.redhat.com/blog/2014/11/up-and-
> running-with-ovirt-3-5-part-two/)  for setting up CTDB and had already
> created hostnames for the floating IP when I decided to ditch that and go
> with the hosts file hack. I already had the volumes mounted on those
> hostnames but you are absolutely right, simply using localhost would be the
> best option.
>
oVirt 3.5? 2014? That's oooold. Both oVirt & Gluster have moved on a lot
since then. I would strongly recommend studying Gluster's documentation
before implementing it in production. It's not complicated, but you have to
have a good understanding of what you're doing & why if you want to protect
the integrity of your data & avoid waking up one day to find everything in
meltdown.

https://gluster.readthedocs.io/en/latest/

Red Hat's portal is also very good & full of detailed tips for tuning your
setup, however their "stable" versions (which they have to support) are of
course much older than the project's own latest stable, so keep this in
mind when considering their advice.

https://access.redhat.com/documentation/en/red-hat-storage/

Likewise with their oVirt documentation, although their supported oVirt
versions are much closer to the current stable release. It also features a
lot of very good advice for configuring & tuning an oVirt (RHEV) &
GlusterFS (RHGS) hyperconverged setup.

https://access.redhat.com/documentation/en/red-hat-virtualization/

For any other Gluster specific questions, you can usually get good & timely
responses on their mailing list & IRC channel.

Thank you for your suggested outline of how to power up/down the cluster, I
> hadn't considered the fact that turning on two out of date nodes would
> clobber data on the new node. This is something I will need to be very
> careful to avoid. The setup is mostly for lab work so not really mission
> critical but I do run a few VM's (freeIPA, GitLab and pfSense) that I'd
> like to keep up 24/7. I make regular backups (outside of ovirt) of those
> just in case.
>
> Thanks, I will do some reading on how gluster handles quorum and heal
> operations but your procedure sounds like a sensible way to operate this
> cluster.
>
> Regards,
>
> Chris.
>
>
> On 2017-02-11 18:08, Doug Ingham wrote:
>
>
>
> On 11 February 2017 at 13:32, Bartosiak-Jentys, Chris <
> chris.bartosiak-jentys at certico.co.uk> wrote:
>
>> Hello list,
>>
>> Just wanted to get your opinion on my ovirt home lab setup. While this is
>> not a production setup I would like it to run relatively reliably so please
>> tell me if the following storage configuration is likely to result in
>> corruption or just bat s**t insane.
>>
>> I have a 3 node hosted engine setup, VM data store and engine data store
>> are both replica 3 gluster volumes (one brick on each host).
>> I do not want to run all 3 hosts 24/7 due to electricity costs, I only
>> power up the larger hosts (2 Dell R710's) when I need additional resources
>> for VM's.
>>
>> I read about using CTDB and floating/virtual IP's to allow the storage
>> mount point to transition between available hosts but after some thought
>> decided to go about this another, simpler, way:
>>
>> I created a common hostname for the storage mount points: gfs-data and
>> gfs-engine
>>
>> On each host I edited /etc/hosts file to have these hostnames resolve to
>> each hosts IP i.e. on host1 gfs-data & gfs-engine --> host1 IP
>> on host2 gfs-data & gfs-engine --> host2 IP
>> etc.
>>
>> In ovirt engine each storage domain is mounted as gfs-data:/data and
>> gfs-engine:/engine
>> My thinking is that this way no matter which host is up and acting as SPM
>> it will be able to mount the storage as its only dependent on that host
>> being up.
>>
>> I changed gluster options for server-quorum-ratio so that the volumes
>> remain up even if quorum is not met, I know this is risky but its just a
>> lab setup after all.
>>
>> So, any thoughts on the /etc/hosts method to ensure the storage mount
>> point is always available? Is data corruption more or less inevitable with
>> this setup? Am I insane ;) ?
>
>
> Why not just use localhost? And no need for CTDB with a floating IP, oVirt
> uses libgfapi for Gluster which deals with that all natively.
>
> As for the quorum issue, I would most definitely *not* run with quorum
> disabled when you're running more than one node. As you say you
> specifically plan for when the other 2 nodes of the replica 3 set will be
> active or not, I'd do something along the lines of the following...
>
> Going from 3 nodes to 1 node:
>  - Put nodes 2 & 3 in maintenance to offload their virtual load;
>  - Once the 2 nodes are free of load, disable quorum on the Gluster
> volumes;
>  - Power down the 2 nodes.
>
> Going from 1 node to 3 nodes:
>  - Power on *only* 1 of the pair of nodes (if you power on both &
> self-heal is enabled, Gluster will "heal" the files on the main node with
> the older files on the 2 nodes which were powered down);
>  - Allow Gluster some time to detect that the files are in split-brain;
>  - Tell Gluster to heal the files in split-brain based on modification
> time;
>  - Once the 2 nodes are in sync, re-enable quorum & power on the last
> node, which will be resynchronised automatically;
>  - Take the 2 hosts out of maintenance mode.
>
> If you want to power on the 2nd two nodes at the same time, make
> absolutely sure self-heal is disabled first! If you don't, Gluster will see
> the 2nd two nodes as in quorum & heal the data on your 1st node with the
> out-of-date data.
>
>
> --
> Doug
>
> --
>
> Chris Bartosiak-Jentys
> Certico
> Tel: 03333 444 884
> Mob: 077 0246 8132
> e-mail: chris at certico.co.uk
> www.certico.co.uk
>
> ------------------------------
>
> Confidentiality Notice: the information contained in this email and any attachments may be legally privileged and confidential.
> If you are not an intended recipient, you are hereby notified that any dissemination, distribution, or copying of this e-mail is strictly prohibited.
> If you have received this e-mail in error, please notify the sender and permanently delete the e-mail and any attachments immediately.
> You should not retain, copy or use this e-mail or any attachments for any purpose, nor disclose all or any part of the contents to any other person.
> Certico is a trading name of "Certico Trading Limited" England & Wales registered company no. 5819172.
>
>

-- 
Doug

On 11 February 2017 at 15:39, Bartosiak-Jentys, Chris <
chris.bartosiak-jentys at certico.co.uk> wrote:

> Thank you for your reply Doug,
>
> I didn't use localhost as I was preparing to follow instructions (blog
> post: http://community.redhat.com/blog/2014/11/up-and-
> running-with-ovirt-3-5-part-two/)  for setting up CTDB and had already
> created hostnames for the floating IP when I decided to ditch that and go
> with the hosts file hack. I already had the volumes mounted on those
> hostnames but you are absolutely right, simply using localhost would be the
> best option.
>
> Thank you for your suggested outline of how to power up/down the cluster,
> I hadn't considered the fact that turning on two out of date nodes would
> clobber data on the new node. This is something I will need to be very
> careful to avoid. The setup is mostly for lab work so not really mission
> critical but I do run a few VM's (freeIPA, GitLab and pfSense) that I'd
> like to keep up 24/7. I make regular backups (outside of ovirt) of those
> just in case.
>
> Thanks, I will do some reading on how gluster handles quorum and heal
> operations but your procedure sounds like a sensible way to operate this
> cluster.
>
> Regards,
>
> Chris.
>
>
> On 2017-02-11 18:08, Doug Ingham wrote:
>
>
>
> On 11 February 2017 at 13:32, Bartosiak-Jentys, Chris <
> chris.bartosiak-jentys at certico.co.uk> wrote:
>
>> Hello list,
>>
>> Just wanted to get your opinion on my ovirt home lab setup. While this is
>> not a production setup I would like it to run relatively reliably so please
>> tell me if the following storage configuration is likely to result in
>> corruption or just bat s**t insane.
>>
>> I have a 3 node hosted engine setup, VM data store and engine data store
>> are both replica 3 gluster volumes (one brick on each host).
>> I do not want to run all 3 hosts 24/7 due to electricity costs, I only
>> power up the larger hosts (2 Dell R710's) when I need additional resources
>> for VM's.
>>
>> I read about using CTDB and floating/virtual IP's to allow the storage
>> mount point to transition between available hosts but after some thought
>> decided to go about this another, simpler, way:
>>
>> I created a common hostname for the storage mount points: gfs-data and
>> gfs-engine
>>
>> On each host I edited /etc/hosts file to have these hostnames resolve to
>> each hosts IP i.e. on host1 gfs-data & gfs-engine --> host1 IP
>> on host2 gfs-data & gfs-engine --> host2 IP
>> etc.
>>
>> In ovirt engine each storage domain is mounted as gfs-data:/data and
>> gfs-engine:/engine
>> My thinking is that this way no matter which host is up and acting as SPM
>> it will be able to mount the storage as its only dependent on that host
>> being up.
>>
>> I changed gluster options for server-quorum-ratio so that the volumes
>> remain up even if quorum is not met, I know this is risky but its just a
>> lab setup after all.
>>
>> So, any thoughts on the /etc/hosts method to ensure the storage mount
>> point is always available? Is data corruption more or less inevitable with
>> this setup? Am I insane ;) ?
>
>
> Why not just use localhost? And no need for CTDB with a floating IP, oVirt
> uses libgfapi for Gluster which deals with that all natively.
>
> As for the quorum issue, I would most definitely *not* run with quorum
> disabled when you're running more than one node. As you say you
> specifically plan for when the other 2 nodes of the replica 3 set will be
> active or not, I'd do something along the lines of the following...
>
> Going from 3 nodes to 1 node:
>  - Put nodes 2 & 3 in maintenance to offload their virtual load;
>  - Once the 2 nodes are free of load, disable quorum on the Gluster
> volumes;
>  - Power down the 2 nodes.
>
> Going from 1 node to 3 nodes:
>  - Power on *only* 1 of the pair of nodes (if you power on both &
> self-heal is enabled, Gluster will "heal" the files on the main node with
> the older files on the 2 nodes which were powered down);
>  - Allow Gluster some time to detect that the files are in split-brain;
>  - Tell Gluster to heal the files in split-brain based on modification
> time;
>  - Once the 2 nodes are in sync, re-enable quorum & power on the last
> node, which will be resynchronised automatically;
>  - Take the 2 hosts out of maintenance mode.
>
> If you want to power on the 2nd two nodes at the same time, make
> absolutely sure self-heal is disabled first! If you don't, Gluster will see
> the 2nd two nodes as in quorum & heal the data on your 1st node with the
> out-of-date data.
>
>
> --
> Doug
>
> --
>
> Chris Bartosiak-Jentys
> Certico
> Tel: 03333 444 884
> Mob: 077 0246 8132
> e-mail: chris at certico.co.uk
> www.certico.co.uk
>
> ------------------------------
>
> Confidentiality Notice: the information contained in this email and any attachments may be legally privileged and confidential.
> If you are not an intended recipient, you are hereby notified that any dissemination, distribution, or copying of this e-mail is strictly prohibited.
> If you have received this e-mail in error, please notify the sender and permanently delete the e-mail and any attachments immediately.
> You should not retain, copy or use this e-mail or any attachments for any purpose, nor disclose all or any part of the contents to any other person.
> Certico is a trading name of "Certico Trading Limited" England & Wales registered company no. 5819172.
>
>

-- 
Doug
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