feat(xo-server/Xapi#_assertHealthyVdiChains): configurable tolerance (#4651)

Fixes #4124

Related to xoa-support#1921

Only configurable globally (not per backup job) for the moment with the `xapiOptions.maxUncoalescedVdis` setting.

CHANGELOG.unreleased.md

@@ -8,6 +8,7 @@
 > Users must be able to say: “Nice enhancement, I'm eager to test it”
 
 - [Logs] Ability to report a bug with attached log (PR [#4201](https://github.com/vatesfr/xen-orchestra/pull/4201))
+- [Backup] Reduce _VDI chain protection error_ occurrence by being more tolerant (configurable via `xo-server`'s `xapiOptions.maxUncoalescedVdis` setting) [#4124](https://github.com/vatesfr/xen-orchestra/issues/4124) (PR [#4651](https://github.com/vatesfr/xen-orchestra/pull/4651))
 
 ### Bug fixes
 

packages/xo-server/config.toml

@@ -94,3 +94,6 @@ timeout = 600e3
 
 # see https:#github.com/vatesfr/xen-orchestra/issues/3419
 # useSudo = false
+
+[xapiOptions]
+maxUncoalescedVdis = 1

packages/xo-server/src/xapi/index.js

@@ -94,10 +94,11 @@ export const IPV6_CONFIG_MODES = ['None', 'DHCP', 'Static', 'Autoconf']
 
 @mixin(mapToArray(mixins))
 export default class Xapi extends XapiBase {
-  constructor({ guessVhdSizeOnImport, ...opts }) {
+  constructor({ guessVhdSizeOnImport, maxUncoalescedVdis, ...opts }) {
     super(opts)
 
     this._guessVhdSizeOnImport = guessVhdSizeOnImport
+    this._maxUncoalescedVdis = maxUncoalescedVdis
 
     // Patch getObject to resolve _xapiId property.
     this.getObject = (getObject => (...args) => {
@@ -724,7 +725,7 @@ export default class Xapi extends XapiBase {
     return promise
   }
 
-  _assertHealthyVdiChain(vdi, cache) {
+  _assertHealthyVdiChain(vdi, cache, tolerance) {
     if (vdi == null) {
       return
     }
@@ -754,7 +755,8 @@ export default class Xapi extends XapiBase {
       const children = childrenMap[vdi.uuid]
       if (
         children.length === 1 &&
-        !children[0].managed // some SRs do not coalesce the leaf
+        !children[0].managed && // some SRs do not coalesce the leaf
+        tolerance-- <= 0
       ) {
         throw new Error('unhealthy VDI chain')
       }
@@ -762,15 +764,16 @@ export default class Xapi extends XapiBase {
 
     this._assertHealthyVdiChain(
       this.getObjectByUuid(vdi.sm_config['vhd-parent'], null),
-      cache
+      cache,
+      tolerance
     )
   }
 
-  _assertHealthyVdiChains(vm) {
+  _assertHealthyVdiChains(vm, tolerance = this._maxUncoalescedVdis) {
     const cache = { __proto__: null }
     forEach(vm.$VBDs, ({ $VDI }) => {
       try {
-        this._assertHealthyVdiChain($VDI, cache)
+        this._assertHealthyVdiChain($VDI, cache, tolerance)
       } catch (error) {
         error.VDI = $VDI
         error.VM = vm