[ovirt-users] Good practices

Mon Aug 7 15:41:17 UTC 2017

Thanks for the clarification Erekle.

However I get surprised with this way of operating from GlusterFS as it 
adds another layer of complexity to the system (either a hardware or 
software RAID) before the gluster config and increase the system's 
overall costs.

An important point to consider is: In RAID configuration you already 
have space 'wasted' in order to build redundancy (either RAID 1, 5, or 
6). Then when you have GlusterFS on the top of several RAIDs you have 
again more data replicated so you end up with the same data consuming 
more space in a group of disks and again on the top of several RAIDs 
depending on the Gluster configuration you have (in a RAID 1 config the 
same data is replicated 4 times).

Yet another downside of having a RAID (specially RAID 5 or 6) is that it 
reduces considerably the write speeds as each group of disks will end up 
having the write speed of a single disk as all other disks of that group 
have to wait for each other to write as well.

Therefore if Gluster already replicates data why does it create this big 
pain you mentioned if the data is replicated somewhere else, can still 
be retrieved to both serve clients and reconstruct the equivalent disk 
when it is replaced ?

Fernando

On 07/08/2017 10:26, Erekle Magradze wrote:
>
> Hi Frenando,
>
> Here is my experience, if you consider a particular hard drive as a 
> brick for gluster volume and it dies, i.e. it becomes not accessible 
> it's a huge hassle to discard that brick and exchange with another 
> one, since gluster some tries to access that broken brick and it's 
> causing (at least it cause for me) a big pain, therefore it's better 
> to have a RAID as brick, i.e. have RAID 1 (mirroring) for each brick, 
> in this case if the disk is down you can easily exchange it and 
> rebuild the RAID without going offline, i.e switching off the volume 
> doing brick manipulations and switching it back on.
>
> Cheers
>
> Erekle
>
>
> On 08/07/2017 03:04 PM, FERNANDO FREDIANI wrote:
>>
>> For any RAID 5 or 6 configuration I normally follow a simple gold 
>> rule which gave good results so far:
>> - up to 4 disks RAID 5
>> - 5 or more disks RAID 6
>>
>> However I didn't really understand well the recommendation to use any 
>> RAID with GlusterFS. I always thought that GlusteFS likes to work in 
>> JBOD mode and control the disks (bricks) directlly so you can create 
>> whatever distribution rule you wish, and if a single disk fails you 
>> just replace it and which obviously have the data replicated from 
>> another. The only downside of using in this way is that the 
>> replication data will be flow accross all servers but that is not 
>> much a big issue.
>>
>> Anyone can elaborate about Using RAID + GlusterFS and JBOD + GlusterFS.
>>
>> Thanks
>> Regards
>> Fernando
>>
>>
>> On 07/08/2017 03:46, Devin Acosta wrote:
>>>
>>> Moacir,
>>>
>>> I have recently installed multiple Red Hat Virtualization hosts for 
>>> several different companies, and have dealt with the Red Hat Support 
>>> Team in depth about optimal configuration in regards to setting up 
>>> GlusterFS most efficiently and I wanted to share with you what I 
>>> learned.
>>>
>>> In general Red Hat Virtualization team frowns upon using each DISK 
>>> of the system as just a JBOD, sure there is some protection by 
>>> having the data replicated, however, the recommendation is to use 
>>> RAID 6 (preferred) or RAID-5, or at least RAID-1 at the very least.
>>>
>>> Here is the direct quote from Red Hat when I asked about RAID and 
>>> Bricks:
>>> /
>>> /
>>> /"A typical Gluster configuration would use RAID underneath the 
>>> bricks. RAID 6 is most typical as it gives you 2 disk failure 
>>> protection, but RAID 5 could be used too. Once you have the RAIDed 
>>> bricks, you'd then apply the desired replication on top of that. The 
>>> most popular way of doing this would be distributed replicated with 
>>> 2x replication. In general you'll get better performance with larger 
>>> bricks. 12 drives is often a sweet spot. Another option would be to 
>>> create a separate tier using all SSD’s.” /
>>>
>>> /In order to SSD tiering from my understanding you would need 1 x 
>>> NVMe drive in each server, or 4 x SSD hot tier (it needs to be 
>>> distributed, replicated for the hot tier if not using NVME). So with 
>>> you only having 1 SSD drive in each server, I’d suggest maybe 
>>> looking into the NVME option. /
>>> /
>>> /
>>> /Since your using only 3-servers, what I’d probably suggest is to do 
>>> (2 Replicas + Arbiter Node), this setup actually doesn’t require the 
>>> 3rd server to have big drives at all as it only stores meta-data 
>>> about the files and not actually a full copy. /
>>> /
>>> /
>>> /Please see the attached document that was given to me by Red Hat to 
>>> get more information on this. Hope this information helps you./
>>> /
>>> /
>>>
>>> --
>>>
>>> Devin Acosta, RHCA, RHVCA
>>> Red Hat Certified Architect
>>>
>>> On August 6, 2017 at 7:29:29 PM, Moacir Ferreira 
>>> (moacirferreira at hotmail.com <mailto:moacirferreira at hotmail.com>) wrote:
>>>
>>>> I am willing to assemble a oVirt "pod", made of 3 servers, each 
>>>> with 2 CPU sockets of 12 cores, 256GB RAM, 7 HDD 10K, 1 SSD. The 
>>>> idea is to use GlusterFS to provide HA for the VMs. The 3 servers 
>>>> have a dual 40Gb NIC and a dual 10Gb NIC. So my intention is to 
>>>> create a loop like a server triangle using the 40Gb NICs for 
>>>> virtualization files (VMs .qcow2) access and to move VMs around the 
>>>> pod (east /west traffic) while using the 10Gb interfaces for giving 
>>>> services to the outside world (north/south traffic).
>>>>
>>>>
>>>> This said, my first question is: How should I deploy GlusterFS in 
>>>> such oVirt scenario? My questions are:
>>>>
>>>>
>>>> 1 - Should I create 3 RAID (i.e.: RAID 5), one on each oVirt node, 
>>>> and then create a GlusterFS using them?
>>>>
>>>> 2 - Instead, should I create a JBOD array made of all server's disks?
>>>>
>>>> 3 - What is the best Gluster configuration to provide for HA while 
>>>> not consuming too much disk space?
>>>>
>>>> 4 - Does a oVirt hypervisor pod like I am planning to build, and 
>>>> the virtualization environment, benefits from tiering when using a 
>>>> SSD disk? And yes, will Gluster do it by default or I have to 
>>>> configure it to do so?
>>>>
>>>>
>>>> At the bottom line, what is the good practice for using GlusterFS 
>>>> in small pods for enterprises?
>>>>
>>>>
>>>> You opinion/feedback will be really appreciated!
>>>>
>>>> Moacir
>>>>
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