If you can accept the failure domain, we find 12:1 ratio of SATA spinners to a 400GB P3700 is reasonable. Benchmarks can saturate it, but it is entirely bored in our real-world workload and only 30-50% utilized during backfills. I am sure one could go even further than 12:1 if they wanted, but we haven't tested.
On Thu, Jul 9, 2015 at 4:47 AM, Götz Reinicke - IT Koordinator < goetz.reini...@filmakademie.de> wrote: > Hi Christian, > Am 09.07.15 um 09:36 schrieb Christian Balzer: > > > > Hello, > > > > On Thu, 09 Jul 2015 08:57:27 +0200 Götz Reinicke - IT Koordinator wrote: > > > >> Hi again, > >> > >> time is passing, so is my budget :-/ and I have to recheck the options > >> for a "starter" cluster. An expansion next year for may be an openstack > >> installation or more performance if the demands rise is possible. The > >> "starter" could always be used as test or slow dark archive. > >> > >> At the beginning I was at 16SATA OSDs with 4 SSDs for journal per node, > >> but now I'm looking for 12 SATA OSDs without SSD journal. Less > >> performance, less capacity I know. But thats ok! > >> > > Leave the space to upgrade these nodes with SSDs in the future. > > If your cluster grows large enough (more than 20 nodes) even a single > > P3700 might do the trick and will need only a PCIe slot. > > If I get you right, the 12Disk is not a bad idea, if there would be the > need of SSD Journal I can add the PCIe P3700. > > In the 12 OSD Setup I should get 2 P3700 one per 6 OSDs. > > God or bad idea? > > > > >> There should be 6 may be with the 12 OSDs 8 Nodes with a repl. of 2. > >> > > Danger, Will Robinson. > > This is essentially a RAID5 and you're plain asking for a double disk > > failure to happen. > > May be I do not understand that. size = 2 I think is more sort of raid1 > ... ? And why am I asking for for a double disk failure? > > To less nodes, OSDs or because of the size = 2. > > > > > See this recent thread: > > "calculating maximum number of disk and node failure that can be handled > > by cluster with out data loss" > > for some discussion and python script which you will need to modify for > > 2 disk replication. > > > > With a RAID5 failure calculator you're at 1 data loss event per 3.5 > > years... > > > > Thanks for that thread, but I dont get the point out of it for me. > > I see that calculating the reliability is some sort of complex math ... > > >> The workload I expect is more writes of may be some GB of Office files > >> per day and some TB of larger video Files from a few users per week. > >> > >> At the end of this year we calculate to have +- 60 to 80 TB of lager > >> videofiles in that cluster, which are accessed from time to time. > >> > >> Any suggestion on the drop of ssd journals? > >> > > You will miss them when the cluster does write, be it from clients or > when > > re-balancing a lost OSD. > > I can imagine, that I might miss the SSD Journal, but if I can add the > P3700 later I feel comfy with it for now. Budget and evaluation related. > > Thanks for your helpful input and feedback. /Götz > > -- > Götz Reinicke > IT-Koordinator > > Tel. +49 7141 969 82420 > E-Mail goetz.reini...@filmakademie.de > > Filmakademie Baden-Württemberg GmbH > Akademiehof 10 > 71638 Ludwigsburg > www.filmakademie.de > > Eintragung Amtsgericht Stuttgart HRB 205016 > > Vorsitzender des Aufsichtsrats: Jürgen Walter MdL > Staatssekretär im Ministerium für Wissenschaft, > Forschung und Kunst Baden-Württemberg > > Geschäftsführer: Prof. Thomas Schadt > > > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- David Burley NOC Manager, Sr. Systems Programmer/Analyst Slashdot Media e: da...@slashdotmedia.com
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