[lustre-discuss] 1 MDS and 1 OSS

[Dilger, Andreas]

First, to answer Amjad's question - the number of OSS nodes you have depends
on the capacity and performance you need.  For 120TB of total storage (assume 30x4TB drives, or 20x60TB drives) a single OSS is definitely capable of handling this many drives.  I'd also assume you are using 10Gb Ethernet (~= 1GB/s), which  a single OSS should be able to saturate (at either 40MB/s or 60MB/s per data drive with RAID-6 8+2 LUNs).  If you want more capacity or bandwidth, you can add more OSS nodes now or in the future.

As Ravi mentioned, with a single OSS and MDS, you will need to reboot the single server in case of failures instead of having automatic failover, but for some systems this is fine.

Finally, as for whether Lustre on a single MDS+OSS is better than running NFS on a single server, that depends mostly on the application workload.  NFS is easier to administer than Lustre, and will provide better small file performance than Lustre.  NFS also has the benefit that it works with every client available.

Interestingly, there are some workloads that users have reported to us where a single Lustre OSS will perform better than NFS, because Lustre does proper data locking/caching, while NFS has only close-to-open consistency semantics, and cannot cache data on the client for a long time.  Any workloads where there are multiple writers/readers to the same file will just not function properly with NFS.  Lustre will handle a large number of clients better than NFS.  For streaming IO loads, Lustre is better able to saturate the network (though for slower networks this doesn't really make much difference).  Lustre can drive faster networks (e.g. IB) much better with LNet than NFS with IPoIB.

And of course, if you think your performance/capacity needs will increase in the future, then Lustre can easily scale to virtually any size and performance you need, while NFS will not.

In general I wouldn't necessarily recommend Lustre for a single MDS+OSS installation, but this depends on your workload and future plans.

Cheers, Andreas

On Oct 30, 2017, at 15:59, E.S. Rosenberg <esr+lustre at mail.hebrew.edu> wrote:
> 
> Maybe someone can answer this in the context of this question, is there any performance gain over classic filers when you are using only a single OSS?
> 
> On Mon, Oct 30, 2017 at 9:56 AM, Ravi Konila <ravibhatk at gmail.com> wrote:
> Hi Majid
>  
> It is better to go for HA for both OSS and MDS. You would need 2 nos of MDS and 2 nos of OSS (identical configuration).
> Also use latest Lustre 2.10.1 release.
>  
> Regards
> Ravi Konila
>  
>  
>> From: Amjad Syed
>> Sent: Monday, October 30, 2017 1:17 PM
>> To: lustre-discuss at lists.lustre.org
>> Subject: [lustre-discuss] 1 MDS and 1 OSS
>>  
>> Hello
>> We are in process in procuring one small Lustre filesystem giving us 120 TB  of storage using Lustre 2.X.
>> The vendor has proposed only 1 MDS and 1 OSS as a solution.
>> The query we have is that is this configuration enough , or we need more OSS?
>> The MDS and OSS server are identical  with regards to RAM (64 GB) and  HDD (300GB)
>>  
>> Thanks
>> Majid

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation