Hi Dominik, On 04/29/15 19:06, Dominik Hannen wrote: > I had planned to use at maximum 80GB of the available 250GB. > 1 x 16GB OS > 4 x 8, 12 or 16GB partitions for osd-journals. > > For a total SSD Usage of 19.2%, 25.6% or 32% > and over-provisioning of 80.8%, 74.3% or 68%. > > I am relatively certain that those SSDs would last ages with THAT > much over-provisioning. SSD lifespan is mostly linked to the total amount of data written as they make efforts to distribute the writes evenly on all cells. In your case this has nothing to do with over-provisioning and everything to do with the amount of data you will write to the OSDs backed by these journals. Over-provisioning can only be useful if : - your SSD is bad at distributing writes with the space it already has with its own over-provisioning and gets better when you add your own, - you never touched data after the offset where your last partition ends (or used TRIM manually to tell the SSD it's OK to use the cells they are currently on as the SSD sees fit). I see people assuming it's enough to not write on the whole LBA space to automatically get better lifespan through better data redistribution by the SSD. It can only work if the SSD is absolutely sure that the rest of the LBA space is unused. This can only happen if this space as never been written to or TRIM has been used to tell it to the SSD. If you had a filesystem full of data at the end of the SSD and removed it without "trimming" the space, it's as if it's still there from the point of view of your SSD. If you tested the drive with some kind of benchmark, same problem. If you didn't call TRIM yourself on the whole drive, you can't assume that over-provisioning will work. It depends on how the drive as been initialized by the manufacturer and AFAIK you don't have access to this information (I wouldn't be surprised if someone working in marketing at a manufacturer would think a good idea to write a default partition scheme with NTFS filesystems without asking techs to validate the idea and that an intern would use some tools overwriting the whole drive to do it). Even with these precautions I've never seen comparative studies for lifespans of SSD with various levels of manual over-provisioning so I'm not even sure that this technique was ever successful (it can't really do much harm as you don't want your journals to be too big anyway). I would be *very* surprised if the drive would get any performance or life expectancy benefit when used at 19.2% instead of 32% or even 75%... Best regards, Lionel Bouton _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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