Having L2ARC on disks has no benefit at all. It only makes sense if the L2ARC devices are on much faster storage (i.e. SSDs/NVMe) than the rest of the pool. Otherwise, the data could just be read from the disks directly.
Cheers, Andreas On Oct 26, 2017, at 10:13, Mannthey, Keith <[email protected]> wrote: > > I have seen both small and large OST work it just depends on what you want in > the system (Size/Performance/Manageability). Do benchmark both as they will > differ in overall performance some. > > L2arc read cache can help some workloads. It takes multi reads for data to > be moved into the cache so standard benchmarking (IOR and other streaming > benchmarks) won't see much of a change. > > Thanks, > Keith > > -----Original Message----- > From: lustre-discuss [mailto:[email protected]] On > Behalf Of Thomas Roth > Sent: Thursday, October 26, 2017 1:50 AM > To: Lustre Discuss <[email protected]> > Subject: Re: [lustre-discuss] ZFS-OST layout, number of OSTs > > On the other hand if we gather three or four raidz2s into one zpool/OST, loss > of one raidz means loss of a 120-160TB OST. > Around here, this is usually the deciding argument. (Even temporarily taking > down one OST for whatever repairs would take more data offline). > > > How is the general experience with having an l2arc on additional disks? > In my test attempts I did not see much benefit under Lustre. > > With our type of hardware, we do not have room for one drive per (small) > zpool - if there were only one or two zpools per box, this would be possible. > > Regards > Thomas > > On 10/24/2017 09:41 PM, Cory Spitz wrote: >> It’s also worth noting that if you have small OSTs it’s much easier to bump >> into a full OST situation. And specifically, if you singly stripe a file >> the file size is limited by the size of the OST. >> >> -Cory >> > _______________________________________________ > lustre-discuss mailing list > [email protected] > http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org > _______________________________________________ > lustre-discuss mailing list > [email protected] > http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org Cheers, Andreas -- Andreas Dilger Lustre Principal Architect Intel Corporation _______________________________________________ lustre-discuss mailing list [email protected] http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
