And the block size for thick snapshots can be set when using the lvcreate command. And the automatic growing of a snapshot can be configured too in the lvm configuration.
Same issues with both thin and thick, if you run out of space. //T Den ons 23 okt. 2019 kl 13:24 skrev Tomas Dalebjörk < [email protected]>: > 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 <[email protected]>: > >> 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: [email protected] - [email protected] >> GPG public key ID: FF5F32A8 >> >
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