Thanks for the suggestion, Simon. Yes, we’ve looked at that, but we think that we’re going to potentially be in a situation where we’re using fairly big SSDs already. For example, if we bought 30 6.4 TB SSDs rated at 1 DWPD and configured them as 6 4+1P RAID 5 LUNs, then we’d end up with a usable capacity of 6 * 4 * 6 = ~144 TB usable space in our “hot” pool. That would satisfy our capacity needs and also not exceed the 1 DWPD rating of the drives.
BTW, we noticed with one particular vendor that their 3 DWPD drives were exactly 1/3rd the size of their 1 DWPD drives … which makes us wonder if that’s coincidence or not. Anybody know for sure? Thanks… Kevin > On Mar 18, 2019, at 4:13 PM, Simon Thompson <s.j.thomp...@bham.ac.uk> wrote: > > Did you look at pricing larger SSDs than you need and only using partial > capacity to get more DWPD out of them? > > I.e. 1TB drive 3dpwd = 3TBpd > 2TB drive (using 1/2 capacity) = 6TBpd > > Simon > ________________________________________ > From: gpfsug-discuss-boun...@spectrumscale.org > [gpfsug-discuss-boun...@spectrumscale.org] on behalf of Buterbaugh, Kevin L > [kevin.buterba...@vanderbilt.edu] > Sent: 18 March 2019 19:09 > To: gpfsug main discussion list > Subject: Re: [gpfsug-discuss] SSDs for data - DWPD? > > Hi All, > > Just wanted to follow up with the results of my survey … I received a grand > total of two responses (Thanks Alex and John). In their case, they’re using > SSDs with a 10 DWPD rating. > > The motivation behind my asking this question was … money! ;-). Seriously, > 10 DWPD drives are still very expensive, while 3 DWPD drives are > significantly less expensive and 1 DWPD drives are even cheaper still. While > we would NOT feel comfortable using anything less than 10 DWPD drives for > metadata, we’re wondering about using less expensive drives for data. > > For example, let’s just say that you’re getting ready to set up a brand new > GPFS 5 formatted filesystem of 1-2 PB in size. You’re considering having 3 > pools: > > 1) a metadata only system pool of 10 DWPD SSDs. 4K inodes, and a ton of > small files that’ll fit in the inode. > 2) a data only “hot” pool (i.e. the default pool for writes) of SSDs. > 3) a data only “capacity” pool of 12 TB spinning disks. > > And let’s just say that you have looked back at the historical data you’ve > collected and you see that over the last 6 months or so you’ve been averaging > 10-12 TB of data being written into your existing filesystem per day. You > want to do migrations between pools only on the weekends if at all possible. > > 12 * 7 = 84 TB. So if you had somewhere between 125 - 150 TB of SSDs ... 1 > DWPD SSDs … then in theory you should easily be able to handle your > anticipated workload without coming close to exceeding the 1 DWPD rating of > the SSDs. > > However, as the saying goes, while in theory there’s no difference between > theory and practice, in practice there is ... so am I overlooking anything > here from a GPFS perspective??? > > If anybody still wants to respond on the DWPD rating of the SSDs they use for > data, I’m still listening. > > Thanks… > > Kevin > > P.S. I still have a couple of “outstanding issues” to respond to that I’ve > posted to the list about previously: > > 1) the long I/O’s we see occasionally in the output of “mmdiag —iohist” on > our NSD servers. We’re still trying to track that down … it seems to happen > only with a subset of our hardware - most of the time at least - but we’re > still working to track down what triggers it … i.e. at this point I can’t say > whether it’s really the hardware or a user abusing the hardware. > > 2) I promised to post benchmark results of 3 different metadata configs: a) > RAID 1 mirrors, b) a RAID 5 stripe, c) no RAID, but GPFS metadata replication > of 3. That benchmarking has been put on hold for reasons I can’t really > discuss on this mailing list at this time … but hopefully soon. > > I haven’t forgotten the above and will respond back on the list when it’s > appropriate. Thanks... > > On Mar 8, 2019, at 10:24 AM, Buterbaugh, Kevin L > <kevin.buterba...@vanderbilt.edu<mailto:kevin.buterba...@vanderbilt.edu>> > wrote: > > Hi All, > > This is kind of a survey if you will, so for this one it might be best if you > responded directly to me and I’ll summarize the results next week. > > Question 1 - do you use SSDs for data? If not - i.e. if you only use SSDs > for metadata (as we currently do) - thanks, that’s all! If, however, you do > use SSDs for data, please see Question 2. > > Question 2 - what is the DWPD (daily writes per day) of the SSDs that you use > for data? > > Question 3 - is that different than the DWPD of the SSDs for metadata? > > Question 4 - any pertinent information in regards to your answers above (i.e. > if you’ve got a filesystem that data is uploaded to only once and never > modified after that then that’s useful to know!)? > > Thanks… > > Kevin > > — > Kevin Buterbaugh - Senior System Administrator > Vanderbilt University - Advanced Computing Center for Research and Education > kevin.buterba...@vanderbilt.edu<mailto:kevin.buterba...@vanderbilt.edu> - > (615)875-9633 > > > _______________________________________________ > gpfsug-discuss mailing list > gpfsug-discuss at spectrumscale.org > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgpfsug.org%2Fmailman%2Flistinfo%2Fgpfsug-discuss&data=02%7C01%7CKevin.Buterbaugh%40vanderbilt.edu%7C274d56e2906e4df3340a08d6abe6a61e%7Cba5a7f39e3be4ab3b45067fa80faecad%7C0%7C0%7C636885404456477052&sdata=eJ6XKuMQ3H4y8V1kyTd8%2ByGJX0rhlTqfcl0fce14pYA%3D&reserved=0 _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at spectrumscale.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
