Re: [ovirt-users] Best practice for iSCSI storage domains

[Christopher Cox]

On 12/07/2017 01:10 AM, Richard Chan wrote:

What is the best practice for iSCSI storage domains:

Many small targets vs a few large targets?

Specific example: if you wanted a 8TB storage domain would you prepare a 
single 8TB LUN or (for example) 8 x 1 TB LUNs.


There's no "best" answer for this.  However, if you know you're going to 
be doing a ton of VMs (storage), then less is best.  The problem with 
"less" is that you might end up wasting more space for longer periods of 
time.  Not necessarily an issue for subsystems with thin provisioning, 
but just something to be aware of.


The number of virtual disks can get extreme.  And while that's not 
really related to the iSCSI, just getting all those virtual disks online 
(for example, after node maintenance) can get time consuming.


Took me over 30 minutes the other day.

Obviously that tends to get worse as the number of virtual disks increases.

So, there is something to be said about trying to reduce the number of 
virtual disks.


Our standard for new storage domains is 6TB.



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Re: [ovirt-users] Best practice for iSCSI storage domains

[Yaniv Kaul]

On Thu, Dec 7, 2017 at 12:51 PM, Maor Lipchuk  wrote:

> On Thu, Dec 7, 2017 at 9:10 AM, Richard Chan  > wrote:
>
>> What is the best practice for iSCSI storage domains:
>>
>> Many small targets vs a few large targets?
>>
>> Specific example: if you wanted a 8TB storage domain would you prepare a
>> single 8TB LUN or (for example) 8 x 1 TB LUNs.
>>
>
> There could be many reasons to use each type.
> From the top of my head I think that configuration wise it will be better
> to configure more than one lun.
> That can be helpful if you plan to use external LUN disks for example.
>
> Multiple targets might also come useful if you plan to configure iSCSI
> multipath in the future, that way you can choose only part of the targets
> to apply the MPIO on.
>

That only makes configuration more complex.
I think for 8TB, a single LUN should suffice.
Y.


>
>
>>
>>
>>
>>
>> --
>> Richard Chan
>>
>>
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Re: [ovirt-users] Best practice for iSCSI storage domains

[FERNANDO FREDIANI]

That's one of the reasons I prefer File storage (like NFS) than iSCSI or 
Fiberchannel. A lot more flexible and manageable.


In the past for VMFS5 I used to work with 4TB LUNs. Now a days something 
between 4TB and 8TB may be ok given the bigger size of VMs, depending on 
your enviroment of course. However one thing to take attention in this 
scenario is how the metadata update process and how that can impact 
performance on bigger LUNs.


Fernando


On 07/12/2017 08:51, Maor Lipchuk wrote:
On Thu, Dec 7, 2017 at 9:10 AM, Richard Chan 
mailto:rich...@treeboxsolutions.com>> 
wrote:


What is the best practice for iSCSI storage domains:

Many small targets vs a few large targets?

Specific example: if you wanted a 8TB storage domain would you
prepare a single 8TB LUN or (for example) 8 x 1 TB LUNs.


There could be many reasons to use each type.
From the top of my head I think that configuration wise it will be 
better to configure more than one lun.

That can be helpful if you plan to use external LUN disks for example.

Multiple targets might also come useful if you plan to configure iSCSI 
multipath in the future, that way you can choose only part of the 
targets to apply the MPIO on.






-- 
Richard Chan



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Re: [ovirt-users] Best practice for iSCSI storage domains

[Maor Lipchuk]

On Thu, Dec 7, 2017 at 9:10 AM, Richard Chan 
wrote:

> What is the best practice for iSCSI storage domains:
>
> Many small targets vs a few large targets?
>
> Specific example: if you wanted a 8TB storage domain would you prepare a
> single 8TB LUN or (for example) 8 x 1 TB LUNs.
>

There could be many reasons to use each type.
>From the top of my head I think that configuration wise it will be better
to configure more than one lun.
That can be helpful if you plan to use external LUN disks for example.

Multiple targets might also come useful if you plan to configure iSCSI
multipath in the future, that way you can choose only part of the targets
to apply the MPIO on.


>
>
>
>
> --
> Richard Chan
>
>
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> Users@ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users
>
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[ovirt-users] Best practice for iSCSI storage domains

[Richard Chan]

What is the best practice for iSCSI storage domains:

Many small targets vs a few large targets?

Specific example: if you wanted a 8TB storage domain would you prepare a
single 8TB LUN or (for example) 8 x 1 TB LUNs.



-- 
Richard Chan
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