Fix volume/stripe calcs when using forced volumes

doc/admin-guide/files/volume.config.en.rst

@@ -68,6 +68,33 @@ sits in front of a volume.  This may be desirable if you are using something lik
 ramdisks, to avoid wasting RAM and cpu time on double caching objects.
 
 
+Exclusive spans and volume sizes
+================================
+
+In the following sample configuration 2 spans `/dev/disk1` and `/dev/disk2` are defined
+in :file:`storage.config`, where span `/dev/disk2` is assigned to `volume 3` exclusively
+(`volume 3` is forced to an "exclusive" span `/dev/disk2`).
+In :file:`volume.config` there are 3 volumes defined, where `volume 1` and `volume 2`
+occupy span `/dev/disk1` taking each 50% of its space and `volume 3` takes 100% of span
+`/dev/disk2` exclusively.
+
+storage.config::
+
+      /dev/disk1
+      /dev/disk2 volume=3 # <- exclusinve span
+
+volume.config::
+
+      volume=1 scheme=http size=50%
+      volume=2 scheme=http size=50%
+      volume=3 scheme=http size=512 # <- volume forced to a specific exclusive span
+
+It is important to note that when percentages are used to specify volume sizes
+and "exclusive" spans are assigned (forced) to a particular volume (in this case `volume 3`),
+the "exclusive" spans (in this case `/dev/disk2`) are excluded from the total cache
+space when the "non-forced" volumes sizes are calculated (in this case `volume 1` and `volume 2`).
+
+
 Examples
 ========
 

iocore/cache/Cache.cc

@@ -2530,6 +2530,8 @@ cplist_init()
   }
 }
 
+static int fillExclusiveDisks(CacheVol *cp);
+
 void
 cplist_update()
 {
@@ -2586,6 +2588,37 @@ cplist_update()
       cp = cp->link.next;
     }
   }
+
+  // Look for (exclusive) spans forced to a specific volume but not yet referenced by any volumes in cp_list,
+  // if found then create a new volume. This also makes sure new exclusive disk volumes are created first
+  // before any other new volumes to assure proper span free space calculation and proper volume block distribution.
+  for (config_vol = config_volumes.cp_queue.head; config_vol; config_vol = config_vol->link.next) {
+    if (nullptr == config_vol->cachep) {
+      // Find out if this is a forced volume assigned exclusively to a span which was cleared (hence not referenced in cp_list).
+      // Note: non-exclusive cleared spans are not handled here, only the "exclusive"
+      for (int d_no = 0; d_no < gndisks; d_no++) {
+        if (gdisks[d_no]->forced_volume_num == config_vol->number) {
+          CacheVol *new_cp = new CacheVol();
+          if (nullptr != new_cp) {
+            new_cp->disk_vols = (DiskVol **)ats_malloc(gndisks * sizeof(DiskVol *));
+            if (nullptr != new_cp->disk_vols) {
+              memset(new_cp->disk_vols, 0, gndisks * sizeof(DiskVol *));
+              new_cp->vol_number = config_vol->number;
+              new_cp->scheme     = config_vol->scheme;
+              config_vol->cachep = new_cp;
+              fillExclusiveDisks(config_vol->cachep);
+              cp_list.enqueue(new_cp);
+            } else {
+              delete new_cp;
+            }
+          }
+        }
+      }
+    } else {
+      // Fill if this is exclusive disk.
+      fillExclusiveDisks(config_vol->cachep);
+    }
+  }
 }
 
 static int
@@ -2599,20 +2632,32 @@ fillExclusiveDisks(CacheVol *cp)
     if (gdisks[i]->forced_volume_num != volume_number) {
       continue;
     }
-    /* The user had created several volumes before - clear the disk
-       and create one volume for http */
-    for (int j = 0; j < static_cast<int>(gdisks[i]->header->num_volumes); j++) {
+
+    /* OK, this should be an "exclusive" disk (span). */
+    diskCount++;
+
+    /* There should be a single "forced" volume and no other volumes should exist on this "exclusive" disk (span) */
+    bool found_nonforced_volumes = false;
+    for (int j = 0; j < (int)gdisks[i]->header->num_volumes; j++) {
       if (volume_number != gdisks[i]->disk_vols[j]->vol_number) {
-        Note("Clearing Disk: %s", gdisks[i]->path);
-        gdisks[i]->delete_all_volumes();
+        found_nonforced_volumes = true;
         break;
       }
     }
-    diskCount++;
+
+    if (found_nonforced_volumes) {
+      /* The user had created several volumes before - clear the disk and create one volume for http */
+      Note("Clearing Disk: %s", gdisks[i]->path);
+      gdisks[i]->delete_all_volumes();
+    } else if (1 == gdisks[i]->header->num_volumes) {
+      /* "Forced" volumes take the whole disk (span) hence nothing more to do for this span. */
+      continue;
+    }
+
+    /* Now, volumes have been either deleted or did not existing to begin with so we need to create them. */
 
     int64_t size_diff = gdisks[i]->num_usable_blocks;
     DiskVolBlock *dpb;
-
     do {
       dpb = gdisks[i]->create_volume(volume_number, size_diff, cp->scheme);
       if (dpb) {
@@ -2628,6 +2673,8 @@ fillExclusiveDisks(CacheVol *cp)
       }
     } while ((size_diff > 0));
   }
+
+  /* Report back the number of disks (spans) that were assigned to volume specified by volume_number. */
   return diskCount;
 }
 
@@ -2692,7 +2739,11 @@ cplist_reconfigure()
     /* sum up the total space available on all the disks.
        round down the space to 128 megabytes */
     for (int i = 0; i < gndisks; i++) {
-      tot_space_in_blks += (gdisks[i]->num_usable_blocks / blocks_per_vol) * blocks_per_vol;
+      // Exclude exclusive disks (with forced volumes) from the following total space calculation,
+      // in such a way forced volumes will not impact volume percentage calculations.
+      if (-1 == gdisks[i]->forced_volume_num) {
+        tot_space_in_blks += (gdisks[i]->num_usable_blocks / blocks_per_vol) * blocks_per_vol;
+      }
     }
 
     double percent_remaining = 100.00;
@@ -2721,16 +2772,8 @@ cplist_reconfigure()
             config_vol->ramcache_enabled);
     }
     cplist_update();
-    /* go through volume config and grow and create volumes */
-
-    for (config_vol = config_volumes.cp_queue.head; config_vol; config_vol = config_vol->link.next) {
-      // if volume is given exclusive disks, fill here and continue
-      if (!config_vol->cachep) {
-        continue;
-      }
-      fillExclusiveDisks(config_vol->cachep);
-    }
 
+    /* go through volume config and grow and create volumes */
     for (config_vol = config_volumes.cp_queue.head; config_vol; config_vol = config_vol->link.next) {
       size = config_vol->size;
       if (size < 128) {