fix: Dynamic snapshot sizing to prevent I/O errors

Problem: Fixed 500MB snapshot size was too small for large/active LVs,
causing I/O errors when snapshot space was exhausted during backup.

Solution: Calculate appropriate snapshot size based on LV size:
- Use 10% of LV size for snapshot space
- Minimum 1GB to handle reasonable activity
- Shows snapshot size in logs for transparency

Example:
- 20GB LV → 2GB snapshot
- 100GB LV → 10GB snapshot
- 500MB LV → 1GB snapshot (minimum)

This prevents snapshot overflow and resulting I/O errors during backup.

Changes:
- GUI: Calculate snapshot size before creating
- CLI: Same dynamic sizing logic
- Both show calculated snapshot size in output
- Handles both single LV and VG backup modes

enhanced_simple_backup.sh

@@ -298,10 +298,21 @@ case "$MODE" in
         SNAPSHOT_NAME="${LV_NAME}_borg_snap"
         SNAPSHOT_PATH="/dev/$VG_NAME/$SNAPSHOT_NAME"
         
+        # Get LV size to determine appropriate snapshot size
+        LV_SIZE_BYTES=$(lvs --noheadings -o lv_size --units b "$SOURCE" | tr -d ' ' | sed 's/B$//')
+        # Use 10% of LV size or minimum 1GB for snapshot
+        SNAPSHOT_SIZE_BYTES=$((LV_SIZE_BYTES / 10))
+        if [ $SNAPSHOT_SIZE_BYTES -lt 1073741824 ]; then
+            SNAPSHOT_SIZE_BYTES=1073741824  # 1GB minimum
+        fi
+        SNAPSHOT_SIZE_GB=$((SNAPSHOT_SIZE_BYTES / 1073741824))
+        SNAPSHOT_SIZE="${SNAPSHOT_SIZE_GB}G"
+        
         info "This will backup LV to Borg repository"
         echo ""
         echo -e "${YELLOW}Source LV: $SOURCE${NC}"
         echo -e "${YELLOW}Repository: $TARGET${NC}"
+        echo -e "${BLUE}Snapshot size: $SNAPSHOT_SIZE${NC}"
         if [ "$NEW_REPO" = true ]; then
             echo -e "${BLUE}Will create new repository${NC}"
         else
@@ -328,7 +339,7 @@ case "$MODE" in
         fi
         
         log "Creating snapshot of source LV"
-        lvcreate -L1G -s -n "$SNAPSHOT_NAME" "$SOURCE" || error "Failed to create snapshot"
+        lvcreate -L"$SNAPSHOT_SIZE" -s -n "$SNAPSHOT_NAME" "$SOURCE" || error "Failed to create snapshot"
         
         # Create Borg archive
         ARCHIVE_NAME="lv_${LV_NAME}_$(date +%Y%m%d_%H%M%S)"
@@ -398,9 +409,19 @@ case "$MODE" in
             SNAPSHOT_PATH="/dev/$SOURCE/$SNAPSHOT_NAME"
             LV_PATH="/dev/$SOURCE/$LV_NAME"
             
+            # Get LV size to determine appropriate snapshot size
+            LV_SIZE_BYTES=$(lvs --noheadings -o lv_size --units b "$LV_PATH" | tr -d ' ' | sed 's/B$//')
+            # Use 10% of LV size or minimum 1GB for snapshot
+            SNAPSHOT_SIZE_BYTES=$((LV_SIZE_BYTES / 10))
+            if [ $SNAPSHOT_SIZE_BYTES -lt 1073741824 ]; then
+                SNAPSHOT_SIZE_BYTES=1073741824  # 1GB minimum
+            fi
+            SNAPSHOT_SIZE_GB=$((SNAPSHOT_SIZE_BYTES / 1073741824))
+            SNAPSHOT_SIZE="${SNAPSHOT_SIZE_GB}G"
+            
             log "Processing LV: $LV_NAME"
-            log "Creating snapshot: $SNAPSHOT_NAME"
-            lvcreate -L500M -s -n "$SNAPSHOT_NAME" "$LV_PATH" || {
+            log "Creating snapshot: $SNAPSHOT_NAME (size: $SNAPSHOT_SIZE)"
+            lvcreate -L"$SNAPSHOT_SIZE" -s -n "$SNAPSHOT_NAME" "$LV_PATH" || {
                 warn "Failed to create snapshot for $LV_NAME"
                 continue
             }

simple_backup_gui.py

@@ -518,8 +518,19 @@ class SimpleBackupGUI:
         snapshot_name = f"{lv_name}_borg_snap"
         self.current_snapshot = f"/dev/{vg_name}/{snapshot_name}"
         
-        self.log(f"Creating snapshot: {snapshot_name}")
-        success, output = self.run_command(f"lvcreate -L1G -s -n {snapshot_name} {source_lv}")
+        # Get LV size to determine appropriate snapshot size
+        success, lv_size_output = self.run_command(f"lvs --noheadings -o lv_size --units b {source_lv}", show_output=False)
+        if success:
+            lv_size_bytes = int(lv_size_output.strip().replace('B', ''))
+            # Use 10% of LV size or minimum 1GB for snapshot
+            snapshot_size_bytes = max(lv_size_bytes // 10, 1024**3)  # Min 1GB
+            snapshot_size_gb = snapshot_size_bytes // (1024**3)
+            snapshot_size = f"{snapshot_size_gb}G"
+        else:
+            snapshot_size = "2G"  # Default fallback
+        
+        self.log(f"Creating snapshot: {snapshot_name} (size: {snapshot_size})")
+        success, output = self.run_command(f"lvcreate -L{snapshot_size} -s -n {snapshot_name} {source_lv}")
         if not success:
             raise Exception(f"Failed to create snapshot: {output}")
         
@@ -609,9 +620,20 @@ class SimpleBackupGUI:
                 snapshot_path = f"/dev/{source_vg}/{snapshot_name}"
                 lv_path = f"/dev/{source_vg}/{lv_name}"
                 
+                # Get LV size to determine appropriate snapshot size
+                success, lv_size_output = self.run_command(f"lvs --noheadings -o lv_size --units b {lv_path}", show_output=False)
+                if success:
+                    lv_size_bytes = int(lv_size_output.strip().replace('B', ''))
+                    # Use 10% of LV size or minimum 1GB for snapshot
+                    snapshot_size_bytes = max(lv_size_bytes // 10, 1024**3)  # Min 1GB
+                    snapshot_size_gb = snapshot_size_bytes // (1024**3)
+                    snapshot_size = f"{snapshot_size_gb}G"
+                else:
+                    snapshot_size = "2G"  # Default fallback
+                
                 self.log(f"Processing LV: {lv_name}")
-                self.log(f"Creating snapshot: {snapshot_name}")
-                success, output = self.run_command(f"lvcreate -L500M -s -n {snapshot_name} {lv_path}")
+                self.log(f"Creating snapshot: {snapshot_name} (size: {snapshot_size})")
+                success, output = self.run_command(f"lvcreate -L{snapshot_size} -s -n {snapshot_name} {lv_path}")
                 if not success:
                     self.log(f"Warning: Failed to create snapshot for {lv_name}: {output}")
                     continue