Il 2020-09-02 20:38 Roy Sigurd Karlsbakk ha scritto:
Hi all I just wonder how it could be possible some day, some year, to make lvm use tiering. I guess this has been debated numerous times before and I found this lvmts project, but it hasn't been updated for eight years or so.
Hi, having developed and supported file-level form of tiered storage in response to a specific customer request, I have the feeling that tiered storage (both file and block based) is not so useful as it seems. Let me explain why I feel so...
The key difference between caching and tiering is that the former does not increase total available space, while the latter provides as much space as available in each storage tier. For example, 1 TB SSD + 10 TB HDD can be combined for a 11 TB tiered volume.
Tiering is useful when the faster volume provides a significant portion of the total aggregated sum - which is often not the case. In the example above, the SSD only provides a 10% space increase over plain caching. You can argue that one can simple enlarge the performane tier, for example using a 4 TB SSD + 10 TB HDD, but you are now in the ballpark of affording a full-SSD volume - ditching *both* tiering and caching.
That said, LVM already provides the basic building block to provide tiering as you can pvmove between block devices. The difficult thing is how to determine which block to move, and managing them in an automated way.
Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@xxxxxxxxxx - info@xxxxxxxxxx GPG public key ID: FF5F32A8 _______________________________________________ linux-lvm mailing list linux-lvm@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
