I have tested FusionIO together with old thick snapshots. I created the thick snapshot on a separate old traditional SATA drive, just to check if that could be used as a snapshot target for high performance disks; like a Fusion IO card. For those who doesn't know about FusionIO; they can deal with 150-250,000 IOPS.
And to be honest, I couldn't bottle neck the SATA disk I used as a thick snapshot target. The reason for why is simple: - thick snapshots uses sequential write techniques If I would have been using thin snapshots, than the writes would most likely be more randomized on disk, which would have required more spindles to coop with this. Anyhow; I am still eager to hear how to use an external device to import snapshots. And when I say "import"; I am not talking about copyback, more to use to read data from. Regards Tomas Den ons 23 okt. 2019 kl 13:08 skrev Gionatan Danti <g.da...@assyoma.it>: > On 23/10/19 12:46, Zdenek Kabelac wrote: > > Just few 'comments' - it's not really comparable - the efficiency of > > thin-pool metadata outperforms old snapshot in BIG way (there is no > > point to talk about snapshots that takes just couple of MiB) > > Yes, this matches my experience. > > > There is also BIG difference about the usage of old snapshot origin and > > snapshot. > > > > COW of old snapshot effectively cuts performance 1/2 if you write to > > origin. > > If used without non-volatile RAID controller, 1/2 is generous - I > measured performance as low as 1/5 (with fat snapshot). > > Talking about thin snapshot, an obvious performance optimization which > seems to not be implemented is to skip reading source data when > overwriting in larger-than-chunksize blocks. > > For example, consider a completely filled 64k chunk thin volume (with > thinpool having ample free space). Snapshotting it and writing a 4k > block on origin will obviously cause a read of the original 64k chunk, > an in-memory change of the 4k block and a write of the entire modified > 64k block to a new location. But writing, say, a 1 MB block should *not* > cause the same read on source: after all, the read data will be > immediately discarded, overwritten by the changed 1 MB block. > > However, my testing shows that source chunks are always read, even when > completely overwritten. > > Am I missing something? > > -- > Danti Gionatan > Supporto Tecnico > Assyoma S.r.l. - www.assyoma.it > email: g.da...@assyoma.it - i...@assyoma.it > GPG public key ID: FF5F32A8 >
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