>> 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... First, filelevel is usually useless. Say you have 50 VMs with Windows server something. A lot of them are bound to have a ton of equal storage in the same areas, but the file size and content will vary over time. With blocklevel tiering, that could work better. > 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. This is all known. > 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. If you look at IOPS instead of just sequencial speed, you'll see the difference. A set of 10 drives in a RAID-6 will perhaps, maybe, give you 1kIOPS, while a single SSD might give you 50kIOPS or even more. This makes a huge impact. > 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. …which was the reason I asked this question, and which should be quite clear in the original post. Vennlig hilsen roy -- Roy Sigurd Karlsbakk (+47) 98013356 http://blogg.karlsbakk.net/ GPG Public key: http://karlsbakk.net/roysigurdkarlsbakk.pubkey.txt -- Hið góða skaltu í stein höggva, hið illa í snjó rita. _______________________________________________ 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/
