Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Lionel Sausin <ls at numerigraphe.com> wrote: >I wouldn't expect anything like the gains of >bcache/flashcache/enhencio. >Normally internal metadata are just as fast, thanks to the write cache >of your disks and RAID adapter. Those are much faster than SSDs and >metadata are small enough. >However you may benefit from external metadata when your those caches >are saturated by writes (high throughput for a long time). >If you do have an SSD and expect big writes, give it a try and please >tell us if it really makes a difference. > >Lionel Sausin. > >Le 26/02/2013 23:30, James Harper a écrit : >> Smallish SSD's are dirt cheap these days and I have a spare slot in >my servers so I was thinking of putting one in and running bcache >(layering would look like drbd->raid0->bcache->sd[ab]). It's a bit of >mucking around to set up as bcache isn't in the kernel at this time and >is targeted against a kernel version that isn't what Debian uses, so it >seems that maybe for now just putting the metadata on the SSD would be >a much simpler option. >> >> I'm currently using internal metadata, does anyone have any comments >on which would be the best way to go? >> >> Also, is there a procedure for moving metadata from internal to >external? Just a word of warning for anyone who is considering to use SSD's, I was recently bitten by a severe performance degradation by Linux 2.6.26 (specifically the version in debian stable), where SSD performance was reduced to about half that achievable by a single hard drive (yes seriously). There is a simple patch to resolve this, or in my case, I upgraded to 3.2 from backports. Hope this helps someone else quicker than it took me to work it out (using 5 x 480G SSD's in RAID5 and wondering why performance sucked so badly) Regards, Adam -- Adam Goryachev Website Managers www.websitemanagers.com.au