[ovirt-users] storage redundancy in Ovirt

Mon Apr 17 21:23:42 UTC 2017

Nir,

A process can chdir into mount point and then lazy umount it. Filesystem remains mounted while the process exists and current directory is on mounted filesystem.

# struncate -s 1g masterfs.img
# mkfs.ext4 masterfs.img
# mkdir masterfs
# mount -o loop masterfs.img masterfs
# cd masterfs
# umount -l .
# touch file
# ls
# cd ..
# ls masterfs

________________________________
From: Nir Soffer <nsoffer at redhat.com>
Sent: Apr 17, 2017 8:40 PM
To: Adam Litke; Pavel Gashev
Cc: users
Subject: Re: [ovirt-users] storage redundancy in Ovirt

On Mon, Apr 17, 2017 at 6:54 PM Adam Litke <alitke at redhat.com<mailto:alitke at redhat.com>> wrote:
On Mon, Apr 17, 2017 at 11:04 AM, Pavel Gashev <Pax at acronis.com<mailto:Pax at acronis.com>> wrote:
Adam,

You know, Sanlock has recovery mechanism that kills VDSM, or even triggers Watchdog to reboot SPM host in case it has lost the SPM lock.
I’m asking because I had issues with my master storage that caused SPM host to reboot by Watchdog. And I was sure that it’s an intended behaviour. Isn’t it?

Yes of course.  But an SPM host can fail but still maintain its connection to the storage lease.  In this case still you need classic fencing.

Something new we are investigating is the use of sanlock's request feature which allows a new host to take the lease away from the current holder.  The current holder would be fenced by sanlock (watchdog if necessary) and only once the lease is free would it be granted to the new requester.

We can use the SPM lease to kill vdsm on the non-responsive SPM host,
and start the SPM on another host, similar to the way we handle vms with
a lease.

But this does not help with the masterfs mounted on the SPM host. if vdsm
is killed before it unmount it, strating the SPM on another host (and mounting
the msasterfs on the new host) will corrupt the masterfs.

When using file based storage (nfs, glusterfs) we don't have a masterfs so
killing vdsm on the SPM should be good enough to start the SPM on another
host, even if fencing is not possible.

We can start with enabling sanlock based SPM fencing on file based storage.

Nir

From: Adam Litke <alitke at redhat.com<mailto:alitke at redhat.com>>
Date: Monday, 17 April 2017 at 17:32
To: Pavel Gashev <Pax at acronis.com<mailto:Pax at acronis.com>>
Cc: Nir Soffer <nsoffer at redhat.com<mailto:nsoffer at redhat.com>>, users <users at ovirt.org<mailto:users at ovirt.org>>

Subject: Re: [ovirt-users] storage redundancy in Ovirt

On Mon, Apr 17, 2017 at 9:26 AM, Pavel Gashev <Pax at acronis.com<mailto:Pax at acronis.com>> wrote:
Nir,

Isn’t SPM managed via Sanlock? I believe there is no need to fence SPM host. Especially if there are no SPM tasks running.

It's true that the exclusivity of the SPM role is enforced by Sanlock but you always need to fence a non-responsive SPM because there is no way to guarantee that the host is not still manipulating storage (eg. LV extensions) and we must ensure that only one host has the masterfs on the master storage domain mounted.

From: <users-bounces at ovirt.org<mailto:users-bounces at ovirt.org>> on behalf of Nir Soffer <nsoffer at redhat.com<mailto:nsoffer at redhat.com>>
Date: Monday, 17 April 2017 at 16:06
To: Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>>, Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>>
Cc: users <users at ovirt.org<mailto:users at ovirt.org>>, FERNANDO FREDIANI <fernando.frediani at upx.com<mailto:fernando.frediani at upx.com>>
Subject: Re: [ovirt-users] storage redundancy in Ovirt

On Mon, Apr 17, 2017 at 8:24 AM Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
But actually, it didn't work well. After main SPM host went down I see this

2017-04-17 05:23:15,554Z ERROR [org.ovirt.engine.core.vdsbroker.irsbroker.IrsProxy] (DefaultQuartzScheduler5) [4dcc033d-26bf-49bb-bfaa-03a970dbbec1] SPM Init: could not find reported vds or not up - pool: 'STG' vds_spm_id: '1'
2017-04-17 05:23:15,567Z INFO  [org.ovirt.engine.core.vdsbroker.irsbroker.IrsProxy] (DefaultQuartzScheduler5) [4dcc033d-26bf-49bb-bfaa-03a970dbbec1] SPM selection - vds seems as spm 'tank5'
2017-04-17 05:23:15,567Z WARN  [org.ovirt.engine.core.vdsbroker.irsbroker.IrsProxy] (DefaultQuartzScheduler5) [4dcc033d-26bf-49bb-bfaa-03a970dbbec1] spm vds is non responsive, stopping spm selection.

So that means only if BMC is up it's possible to automatically switch  SPM host?

BMC?

If your SPM is no responsive, the system will try to fence it. Did you
configure power management for all hosts? did you check that it
work? How did you simulate non-responsive host?

If power management is not configured or fail, the system cannot
move the spm to another host, unless you manually confirm that the
SPM host was rebooted.

Nir

Thanks

On Sun, Apr 16, 2017 at 8:29 PM, Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
Oh, fence agent works fine if I select ilo4,
Thank you for your help!

On Sun, Apr 16, 2017 at 8:22 PM Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>> wrote:
On Sun, Apr 16, 2017 at 11:19 PM, Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
Makes sense.
I was trying to set it up, but doesn't work with our staging hardware.
We have old ilo100, I'll try again.
Thanks!

It is absolutely necessary for any HA to work properly. There's of course the "confirm host has been shutdown" option, which serves as an override for the fence command, but it's manual

On Sun, Apr 16, 2017 at 8:18 PM Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>> wrote:
On Sun, Apr 16, 2017 at 11:15 PM, Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
Fence agent under each node?

When you configure a host, there's the power management tab, where you need to enter the bmc details for the host. If you don't have fencing enabled, how do you expect the system to make sure a host running a service is actually down (and it is safe to start HA services elsewhere), and not, for example, just unreachable by the engine? How do you avoid a splitbraid -> SBA ?

On Sun, Apr 16, 2017 at 8:14 PM Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>> wrote:
On Sun, Apr 16, 2017 at 11:13 PM, Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
"Corner cases"?
I tried to simulate crash of SPM server and ovirt kept trying to reistablished connection to the failed node.

Did you configure fencing?

On Sun, Apr 16, 2017 at 8:10 PM Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>> wrote:
On Sun, Apr 16, 2017 at 7:29 AM, Nir Soffer <nsoffer at redhat.com<mailto:nsoffer at redhat.com>> wrote:
On Sun, Apr 16, 2017 at 2:05 PM Dan Yasny <dyasny at redhat.com<mailto:dyasny at redhat.com>> wrote:

On Apr 16, 2017 7:01 AM, "Nir Soffer" <nsoffer at redhat.com<mailto:nsoffer at redhat.com>> wrote:
On Sun, Apr 16, 2017 at 4:17 AM Dan Yasny <dyasny at gmail.com<mailto:dyasny at gmail.com>> wrote:
When you set up a storage domain, you need to specify a host to perform the initial storage operations, but once the SD is defined, it's details are in the engine database, and all the hosts get connected to it directly. If the first host you used to define the SD goes down, all other hosts will still remain connected and work. SPM is an HA service, and if the current SPM host goes down, SPM gets started on another host in the DC. In short, unless your actual NFS exporting host goes down, there is no outage.

There is no storage outage, but if you shutdown the spm host, the spm host
will not move to a new host until the spm host is online again, or you confirm
manually that the spm host was rebooted.

In a properly configured setup the SBA should take care of that. That's the whole point of HA services

In some cases like power loss or hardware failure, there is no way to start
the spm host, and the system cannot recover automatically.

There are always corner cases, no doubt. But in a normal situation. where an SPM host goes down because of a hardware failure, it gets fenced, other hosts contend for SPM and start it. No surprises there.

Nir

Nir

On Sat, Apr 15, 2017 at 1:53 PM, Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>> wrote:
Hi Fernando,
I see each host has direct connection nfs mount, but yes, if main host to which I connected nfs storage going down the storage becomes unavailable and all vms are down

On Sat, Apr 15, 2017 at 10:37 AM FERNANDO FREDIANI <fernando.frediani at upx.com<mailto:fernando.frediani at upx.com>> wrote:
Hello Konstantin.
That doesn`t make much sense make a whole cluster depend on a single host. >From what I know any host talk directly to NFS Storage Array or whatever other Shared Storage you have.
Have you tested that host going down if that affects the other with the NFS mounted directlly in a NFS Storage array ?
Fernando

2017-04-15 12:42 GMT-03:00 Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>>:
In ovirt you have to attach storage through specific host.
If host goes down storage is not available.

On Sat, Apr 15, 2017 at 7:31 AM FERNANDO FREDIANI <fernando.frediani at upx.com<mailto:fernando.frediani at upx.com>> wrote:
Well, make it not go through host1 and dedicate a storage server for running NFS and make both hosts connect to it.
In my view NFS is much easier to manage than any other type of storage, specially FC and iSCSI and performance is pretty much the same, so you won`t get better results other than management going to other type.
Fernando

2017-04-15 5:25 GMT-03:00 Konstantin Raskoshnyi <konrasko at gmail.com<mailto:konrasko at gmail.com>>:
Hi guys,
I have one nfs storage,
it's connected through host1.
host2 also has access to it, I can easily migrate vms between them.

The question is - if host1 is down - all infrastructure is down, since all traffic goes through host1,
is there any way in oVirt to use redundant storage?

Only glusterfs?

Thanks

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Adam Litke

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Adam Litke
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