Hi Bob, If you mean #4 with 2x data replication...then I would be very wary as the chance of data loss would be very high given local disk failure rates. So I think its really #4 with 3x replication vs #3 with 2x replication (and raid5/6 in node) (with maybe 3x for metadata). The space overhead is somewhat similar, but the rebuild times should be much faster for #3 given that a failed disk will not place any load on the storage network (as well there will be less data placed on network).
Dean From: "Oesterlin, Robert" <[email protected]> To: gpfsug main discussion list <[email protected]> Date: 12/01/2016 04:48 AM Subject: Re: [gpfsug-discuss] Strategies - servers with local SAS disks Sent by: [email protected] Some interesting discussion here. Perhaps I should have been a bit clearer on what I’m looking at here: I have 12 servers with 70*4TB drives each – so the hardware is free. What’s the best strategy for using these as GPFS NSD servers, given that I don’t want to relay on any “bleeding edge” technologies. 1) My first choice would be GNR on commodity hardware – if IBM would give that to us. :-) 2) Use standard RAID groups with no replication – downside is data availability of you lose an NSD and RAID group rebuild time with large disks 3) RAID groups with replication – but I lose a LOT of space (20% for RAID + 50% of what’s left for replication) 4) No raid groups, single NSD per disk, single failure group per servers, replication. Downside here is I need to restripe every time a disk fails to get the filesystem back to a good state. Might be OK using QoS to get the IO impact down 5) FPO doesn’t seem to by me anything, as these are straight NSD servers and no computation is going on these servers, and I still must live with the re-stripe. Option (4) seems the best of the “no great options” I have in front of me. Bob Oesterlin Sr Principal Storage Engineer, Nuance From: <[email protected]> on behalf of Zachary Giles <[email protected]> Reply-To: gpfsug main discussion list <[email protected]> Date: Wednesday, November 30, 2016 at 10:27 PM To: gpfsug main discussion list <[email protected]> Subject: [EXTERNAL] Re: [gpfsug-discuss] Strategies - servers with local SAS disks Aaron, Thanks for jumping onboard. It's nice to see others confirming this. Sometimes I feel alone on this topic. It's should also be possible to use ZFS with ZVOLs presented as block devices for a backing store for NSDs. I'm not claiming it's stable, nor a good idea, nor performant.. but should be possible. :) There are various reports about it. Might be at least worth looking in to compared to Linux "md raid" if one truly needs an all-software solution that already exists. Something to think about and test over. On Wed, Nov 30, 2016 at 11:15 PM, Aaron Knister <[email protected]> wrote: Thanks Zach, I was about to echo similar sentiments and you saved me a ton of typing :) Bob, I know this doesn't help you today since I'm pretty sure its not yet available, but if one scours the interwebs they can find mention of something called Mestor. There's very very limited information here: - https://indico.cern.ch/event/531810/contributions/2306222/attachments/1357265/2053960/Spectrum_Scale-HEPIX_V1a.pdf - https://www.yumpu.com/en/document/view/5544551/ibm-system-x-gpfs-storage-server-stfc (slide 20) Sounds like if it were available it would fit this use case very well. I also had preliminary success with using sheepdog ( https://sheepdog.github.io/sheepdog/) as a backing store for GPFS in a similar situation. It's perhaps at a very high conceptually level similar to Mestor. You erasure code your data across the nodes w/ the SAS disks and then present those block devices to your NSD servers. I proved it could work but never tried to to much with it because the requirements changed. My money would be on your first option-- creating local RAIDs and then replicating to give you availability in the event a node goes offline. -Aaron On 11/30/16 10:59 PM, Zachary Giles wrote: Just remember that replication protects against data availability, not integrity. GPFS still requires the underlying block device to return good data. If you're using it on plain disks (SAS or SSD), and the drive returns corrupt data, GPFS won't know any better and just deliver it to the client. Further, if you do a partial read followed by a write, both replicas could be destroyed. There's also no efficient way to force use of a second replica if you realize the first is bad, short of taking the first entirely offline. In that case while migrating data, there's no good way to prevent read-rewrite of other corrupt data on your drive that has the "good copy" while restriping off a faulty drive. Ideally RAID would have a goal of only returning data that passed the RAID algorithm, so shouldn't be corrupt, or made good by recreating from parity. However, as we all know RAID controllers are definitely prone to failures as well for many reasons, but at least a drive can go bad in various ways (bad sectors, slow, just dead, poor SSD cell wear, etc) without (hopefully) silent corruption.. Just something to think about while considering replication .. On Wed, Nov 30, 2016 at 11:28 AM, Uwe Falke <[email protected] <mailto:[email protected]>> wrote: I have once set up a small system with just a few SSDs in two NSD servers, providin a scratch file system in a computing cluster. No RAID, two replica. works, as long the admins do not do silly things (like rebooting servers in sequence without checking for disks being up in between). Going for RAIDs without GPFS replication protects you against single disk failures, but you're lost if just one of your NSD servers goes off. FPO makes sense only sense IMHO if your NSD servers are also processing the data (and then you need to control that somehow). Other ideas? what else can you do with GPFS and local disks than what you considered? I suppose nothing reasonable ... Mit freundlichen Grüßen / Kind regards Dr. Uwe Falke IT Specialist High Performance Computing Services / Integrated Technology Services / Data Center Services ------------------------------------------------------------------------------------------------------------------------------------------- IBM Deutschland Rathausstr. 7 09111 Chemnitz Phone: +49 371 6978 2165 <tel:%2B49%20371%206978%202165> Mobile: +49 175 575 2877 <tel:%2B49%20175%20575%202877> E-Mail: [email protected] <mailto:[email protected]> ------------------------------------------------------------------------------------------------------------------------------------------- IBM Deutschland Business & Technology Services GmbH / Geschäftsführung: Frank Hammer, Thorsten Moehring Sitz der Gesellschaft: Ehningen / Registergericht: Amtsgericht Stuttgart, HRB 17122 From: "Oesterlin, Robert" <[email protected] <mailto:[email protected]>> To: gpfsug main discussion list <[email protected] <mailto:[email protected]>> Date: 11/30/2016 03:34 PM Subject: [gpfsug-discuss] Strategies - servers with local SAS disks Sent by: [email protected] <mailto:[email protected]> Looking for feedback/strategies in setting up several GPFS servers with local SAS. They would all be part of the same file system. The systems are all similar in configuration - 70 4TB drives. Options I?m considering: - Create RAID arrays of the disks on each server (worried about the RAID rebuild time when a drive fails with 4, 6, 8TB drives) - No RAID with 2 replicas, single drive per NSD. When a drive fails, recreate the NSD ? but then I need to fix up the data replication via restripe - FPO ? with multiple failure groups - letting the system manage replica placement and then have GPFS due the restripe on disk failure automatically Comments or other ideas welcome. Bob Oesterlin Sr Principal Storage Engineer, Nuance 507-269-0413 <tel:507-269-0413> _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org <http://spectrumscale.org> http://gpfsug.org/mailman/listinfo/gpfsug-discuss <http://gpfsug.org/mailman/listinfo/gpfsug-discuss> _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org <http://spectrumscale.org> http://gpfsug.org/mailman/listinfo/gpfsug-discuss <http://gpfsug.org/mailman/listinfo/gpfsug-discuss> -- Zach Giles [email protected] <mailto:[email protected]> _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss -- Aaron Knister NASA Center for Climate Simulation (Code 606.2) Goddard Space Flight Center (301) 286-2776 _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss -- Zach Giles [email protected]_______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
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