Re: [ceph-users] how possible is that ceph cluster crash

Nick Fisk Fri, 18 Nov 2016 16:05:38 -0800

Yes, because these things happen

http://www.theregister.co.uk/2016/11/15/memset_power_cut_service_interruption/


We had customers who had kit in this DC.

To use your analogy, it's like crossing the road at traffic lights butnot checking cars have stopped. You might be OK 99%of the time, butsooner or later it will bite you in the arse and it won't be pretty.


________________________________
From: "Brian ::" <[email protected]>
Sent: 18 Nov 2016 11:52 p.m.
To: [email protected]
Cc: Craig Chi; [email protected]; Nick Fisk
Subject: Re: [ceph-users] how possible is that ceph cluster crash

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This is like your mother telling not to cross the road when you were 4
years of age but not telling you it was because you could be flattened
by a car :)

Can you expand on your answer? If you are in a DC with AB power,
redundant UPS, dual feed from the electric company, onsite generators,
dual PSU servers, is it still a bad idea?




On Fri, Nov 18, 2016 at 6:52 PM, Samuel Just <[email protected]> wrote:

Never *ever* use nobarrier with ceph under *any* circumstances.  I
cannot stress this enough.
-Sam

On Fri, Nov 18, 2016 at 10:39 AM, Craig Chi <[email protected]> wrote:

Hi Nick and other Cephers,

Thanks for your reply.

2) Config Errors
This can be an easy one to say you are safe from. But I would say most
outages and data loss incidents I have seen on the mailing
lists have been due to poor hardware choice or configuring options such as
size=2, min_size=1 or enabling stuff like nobarriers.


I am wondering the pros and cons of the nobarrier option used by Ceph.

It is well known that nobarrier is dangerous when power outage happens, but

if we already have replicas in different racks or PDUs, will Cephreduce the

risk of data lost with this option?

I have seen many performance tuning articles providing nobarrier option in
xfs, but there are not many of then mention the trade-off of nobarrier.

Is it really unacceptable to use nobarrier in productionenvironment? I will

be much grateful if you guys are willing to share any experiences about
nobarrier and xfs.

Sincerely,
Craig Chi (Product Developer)
Synology Inc. Taipei, Taiwan. Ext. 361

On 2016-11-17 05:04, Nick Fisk <[email protected]> wrote:

-----Original Message-----
From: ceph-users [mailto:[email protected]] On Behalf Of
Pedro Benites
Sent: 16 November 2016 17:51
To: [email protected]
Subject: [ceph-users] how possible is that ceph cluster crash

Hi,

I have a ceph cluster with 50 TB, with 15 osds, it is working fine for one
year and I would like to grow it and migrate all my old

storage,

about 100 TB to ceph, but I have a doubt. How possible is that the cluster
fail and everything went very bad?


Everything is possible, I think there are 3 main risks

1) Hardware failure
I would say Ceph is probably one of the safest options in regards to
hardware failures, certainly if you start using 4TB+ disks.

2) Config Errors
This can be an easy one to say you are safe from. But I would say most
outages and data loss incidents I have seen on the mailing
lists have been due to poor hardware choice or configuring options such as
size=2, min_size=1 or enabling stuff like nobarriers.

3) Ceph Bugs
Probably the rarest, but potentially the most scary as you have less
control. They do happen and it's something to be aware of

How reliable is ceph?

What is the risk about lose my data.? is necessary backup my data?


Yes, always backup your data, no matter solution you use. Just like RAID !=
Backup, neither does ceph.


Regards.
Pedro.
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