[Lustre-discuss] MDS failover: SSD+DRDB or shared 15K-SAS-Storage RAID with approx. 10 disks

[Michael Kluge]

Hi Carlos,

> In my experience SSDs didn't help much, since the MDS bottleneck is not
> only a disk problem rather than the entire lustre metadata mechanism.

Yes, but one does not need much space on the MDS and four SSDs (as MDT) 
are way cheaper than a RAID controller with 10 15K disks. So the 
question is basically how the DRDB latency will influence the MDT 
performance. I know sync/async makes a big difference here, but I have 
no idea about the performance impact of both or how the reliability is 
influenced.

> One remark about DRDB: I've seen customers using it, but IMHO, if
> Active/standby HA type configuration would be more reliable and will
> provide you a better resilience. Again, don't know about your uptime and
> reliability needs, but the customers I've worked with that requires
> minimum downtime on production, always go for RAID controllers rather than
> DRDB replication.

OK, thanks. That is a good information. So SSD+DRDB are considered to be 
the "cheap" solution. Even for small clusters?


Regards, Michael

>
> Regards,
> Carlos.
>
>
> --
> Carlos Thomaz | Systems Architect
> Mobile: +1 (303) 519-0578
> cthomaz at ddn.com | Skype ID: carlosthomaz
> DataDirect Networks, Inc.
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>
>
>
>
> On 1/22/12 12:04 PM, "Michael Kluge"<Michael.Kluge at tu-dresden.de>  wrote:
>
>> Hi,
>>
>> I have been asked, which one of the two I would chose for two MDS
>> servers (active/passive). Whether I would like to have SSDs, maybe two
>> (mirrored) in both servers and DRDB for synching, or a RAID controller
>> that has a 15K disks. I have not done benchmarks on this topic myself
>> and would like to ask if anyone has an idea or numbers? The cluster will
>> be pretty small, about 50 clients.
>>
>>
>> Regards, Michael
>>
>> --
>> Dr.-Ing. Michael Kluge
>>
>> Technische Universität Dresden
>> Center for Information Services and
>> High Performance Computing (ZIH)
>> D-01062 Dresden
>> Germany
>>
>> Contact:
>> Willersbau, Room WIL A 208
>> Phone:  (+49) 351 463-34217
>> Fax:    (+49) 351 463-37773
>> e-mail: michael.kluge at tu-dresden.de
>> WWW:    http://www.tu-dresden.de/zih
>> _______________________________________________
>> Lustre-discuss mailing list
>> Lustre-discuss at lists.lustre.org
>> http://lists.lustre.org/mailman/listinfo/lustre-discuss
>

-- 
Dr.-Ing. Michael Kluge

Technische Universität Dresden
Center for Information Services and
High Performance Computing (ZIH)
D-01062 Dresden
Germany

Contact:
Willersbau, Room WIL A 208
Phone:  (+49) 351 463-34217
Fax:    (+49) 351 463-37773
e-mail: michael.kluge at tu-dresden.de
WWW:    http://www.tu-dresden.de/zih