Bug 1335861
| Summary: | Add basic support to LVM for raid0 using the md-based dm-raid kernel target. | ||
|---|---|---|---|
| Product: | [Community] LVM and device-mapper | Reporter: | Alasdair Kergon <agk> |
| Component: | lvm2 | Assignee: | Alasdair Kergon <agk> |
| lvm2 sub component: | Mirroring and RAID | QA Contact: | cluster-qe <cluster-qe> |
| Status: | CLOSED CURRENTRELEASE | Docs Contact: | |
| Severity: | medium | ||
| Priority: | high | CC: | agk, heinzm, jbrassow, msnitzer, prajnoha, teigland, zkabelac |
| Version: | 2.02.153 | Keywords: | FutureFeature |
| Target Milestone: | RHEL 7 | Flags: | agk:
lvm-technical-solution+
rule-engine: lvm-test-coverage? |
| Target Release: | 2016-05 | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Enhancement | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2018-02-12 19:24:42 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | |||
| Bug Blocks: | 1191594, 1390358 | ||
I don't like introducing special lvm2 metadata syntax to
cope with "raid0". Let's use the "raids = ..." one throughout
and avoid adding new syntax when it is not needed:
segment1 {
start_extent = 0
extent_count = 32 # 32 Megabytes
type = "raid0"
stripe_count = 2
stripe_size = 64
raids = [
"-", "lvol0_rimage_0",
"-", "lvol0_rimage_1"
]
}
"raid0_meta" will fit into this populating "-" with
metadata devices instead.
Type "raid0_meta" can use the standard "raids" section, but requiring a special "-" placeholder just looks like unnecessary complexity for humans working with metadata. It's easier for the computer to hide that than to have to explain the difference. (In reply to Alasdair Kergon from comment #2) > Type "raid0_meta" can use the standard "raids" section, but requiring a > special "-" placeholder just looks like unnecessary complexity for humans > working with metadata. It's easier for the computer to hide that than to > have to explain the difference. This tells humans explicitly that there are no metadata devices. We should avoid introducing special cases wherever possible in order to limit syntax proliferation. Using the given "raids = ..." lvm2 metadata syntax does that and keeps the syntax for all dm-raid mappings rather than special casing a particular one. (In reply to Heinz Mauelshagen from comment #3) > (In reply to Alasdair Kergon from comment #2) > > Type "raid0_meta" can use the standard "raids" section, but requiring a > > special "-" placeholder just looks like unnecessary complexity for humans > > working with metadata. It's easier for the computer to hide that than to > > have to explain the difference. > > This tells humans explicitly that there are no metadata devices. > > We should avoid introducing special cases wherever possible in order > to limit syntax proliferation. > > Using the given "raids = ..." lvm2 metadata syntax does that and > keeps the syntax for all dm-raid mappings rather than special > casing a particular one. Agreed. Stick with the current RAID metadata format. RAID0 is part of the same family. Out of curiosity, would it be smart to use s/"-"/"NoMetaLV"/ instead? (In reply to Jonathan Earl Brassow from comment #4) > (In reply to Heinz Mauelshagen from comment #3) > > (In reply to Alasdair Kergon from comment #2) > > > Type "raid0_meta" can use the standard "raids" section, but requiring a > > > special "-" placeholder just looks like unnecessary complexity for humans > > > working with metadata. It's easier for the computer to hide that than to > > > have to explain the difference. > > > > This tells humans explicitly that there are no metadata devices. > > > > We should avoid introducing special cases wherever possible in order > > to limit syntax proliferation. > > > > Using the given "raids = ..." lvm2 metadata syntax does that and > > keeps the syntax for all dm-raid mappings rather than special > > casing a particular one. > > Agreed. Stick with the current RAID metadata format. RAID0 is part of the > same family. > > Out of curiosity, would it be smart to use s/"-"/"NoMetaLV"/ instead? This would enhance human readability but unnecessarily grow the lvm2 test metadata as '-' tells enough. I'd vote for keeping the '-' as we already have it for missing metadata devices. If we did not, we'd even have to think about distinguishing between intentionally avoided metadata devices as with 'raid0' and missing ones due to failed PVs with other raid types to be semantically expressive. Based on a discussion, "" would be preferable to "-" for the non-defined metadata devices, which I'd still prefer over the extra raid0_lvs for this special case Alasdair prefers. I think the general format is nice and clean. The way we typically handle human readability is by adding a comment like # no metadata LV. (In reply to David Teigland from comment #7) > I think the general format is nice and clean. The way we typically handle > human readability is by adding a comment like # no metadata LV. Right, that'd make it clean as with other similarly commented items. Upstream commits bf8d00985ada723778701530c7ea863c617dda8a b896f7de1e6773ce6c17bf29a9123276695f4b60 686acce23fed6bd72af63201e4cc56bc5958379e d8c2677ab92c3c3bd35ccab0d486ebce8db4fbb4 |
Allow the creation and activation of striped volumes using --type raid0. Extend LVM metadata to store raid0 volumes. No raid metadata areas are created. Such LVs may only contain one segment so the number of stripes cannot vary along their length. Kernel target must be version 1.7 or higher. Must not break any existing functionality. Proposed segment metadata: segment1 { start_extent = 0 extent_count = 4 type = "raid0" stripe_count = 2 stripe_size = 128 raid0_lvs = [ "lvol0_rimage_0", "lvol0_rimage_1" ] }