feat: Add --workdir flag for cluster restore

Solves disk space issues on VMs with small system disks but large NFS mounts.

Use case:
- VM has small / partition (e.g., 7.8G with 2.3G used)
- Backup archive on NFS mount (e.g., /u01/dba with 140G free)
- Restore fails: "insufficient disk space: 74.7% used - need at least 4x archive size"

Solution:
- Added --workdir flag to restore cluster command
- Allows specifying alternative extraction directory
- Interactive confirmation required for safety
- Updated error messages with helpful tip

Example:
  dbbackup restore cluster backup.tar.gz --workdir /u01/dba/restore_tmp --confirm

This is environmental, not a bug. Code working brilliantly! 👨‍🍳💋

README.md

@@ -201,6 +201,15 @@ Restore full cluster:
 ./dbbackup restore cluster cluster_backup.tar.gz --confirm
 ```
 
+**For VMs with limited system disk space** (common with NFS-mounted backup storage):
+
+```bash
+# Use NFS mount or larger partition for extraction
+./dbbackup restore cluster cluster_backup.tar.gz --workdir /u01/dba/restore_tmp --confirm
+```
+
+This prevents "insufficient disk space" errors when the backup directory has space but the system root partition is small.
+
 ## Commands
 
 ### Global Flags (Available for all commands)
@@ -1257,7 +1266,7 @@ Enable detailed logging:
 
 - **"Ident authentication failed"** - Run as matching OS user or configure password authentication
 - **"Permission denied"** - Check database user privileges
-- **"Disk space check failed"** - Ensure 4x archive size available
+- **"Disk space check failed"** - Ensure 4x archive size available. For VMs with small system disks, use `--workdir /path/to/larger/partition` to extract on NFS mount or larger disk
 - **"Archive validation failed"** - Backup file corrupted or incomplete
 
 ## Building

cmd/restore.go

@@ -30,6 +30,7 @@ var (
 	restoreTarget    string
 	restoreVerbose   bool
 	restoreNoProgress bool
+	restoreWorkdir   string
 	
 	// Encryption flags
 	restoreEncryptionKeyFile string
@@ -135,6 +136,9 @@ Examples:
 
 	# Use parallel decompression
 	dbbackup restore cluster cluster_backup.tar.gz --jobs 4 --confirm
+
+	# Use alternative working directory (for VMs with small system disk)
+	dbbackup restore cluster cluster_backup.tar.gz --workdir /u01/dba/restore_tmp --confirm
 `,
 	Args: cobra.ExactArgs(1),
 	RunE: runRestoreCluster,
@@ -229,6 +233,7 @@ func init() {
 	restoreClusterCmd.Flags().BoolVar(&restoreDryRun, "dry-run", false, "Show what would be done without executing")
 	restoreClusterCmd.Flags().BoolVar(&restoreForce, "force", false, "Skip safety checks and confirmations")
 	restoreClusterCmd.Flags().IntVar(&restoreJobs, "jobs", 0, "Number of parallel decompression jobs (0 = auto)")
+	restoreClusterCmd.Flags().StringVar(&restoreWorkdir, "workdir", "", "Working directory for extraction (use when system disk is small, e.g. /u01/dba/restore_tmp)")
 	restoreClusterCmd.Flags().BoolVar(&restoreVerbose, "verbose", false, "Show detailed restore progress")
 	restoreClusterCmd.Flags().BoolVar(&restoreNoProgress, "no-progress", false, "Disable progress indicators")
 	restoreClusterCmd.Flags().StringVar(&restoreEncryptionKeyFile, "encryption-key-file", "", "Path to encryption key file (required for encrypted backups)")
@@ -476,9 +481,35 @@ func runRestoreCluster(cmd *cobra.Command, args []string) error {
 			return fmt.Errorf("archive validation failed: %w", err)
 		}
 
+		// Determine where to check disk space
+		checkDir := cfg.BackupDir
+		if restoreWorkdir != "" {
+			checkDir = restoreWorkdir
+			
+			// Verify workdir exists or create it
+			if _, err := os.Stat(restoreWorkdir); os.IsNotExist(err) {
+				log.Warn("Working directory does not exist, will be created", "path", restoreWorkdir)
+				if err := os.MkdirAll(restoreWorkdir, 0755); err != nil {
+					return fmt.Errorf("cannot create working directory: %w", err)
+				}
+			}
+			
+			log.Warn("⚠️  Using alternative working directory for extraction")
+			log.Warn("    This is recommended when system disk space is limited")
+			log.Warn("    Location: " + restoreWorkdir)
+			
+			// Interactive confirmation required
+			if !restoreConfirm {
+				fmt.Printf("\n⚠️  Alternative extraction directory: %s\n", restoreWorkdir)
+				fmt.Printf("   This location will be used for temporary extraction.\n")
+				fmt.Printf("   Add --confirm flag to proceed.\n\n")
+				return fmt.Errorf("confirmation required for --workdir usage")
+			}
+		}
+
 		log.Info("Checking disk space...")
 		multiplier := 4.0 // Cluster needs more space for extraction
-		if err := safety.CheckDiskSpace(archivePath, multiplier); err != nil {
+		if err := safety.CheckDiskSpaceAt(archivePath, checkDir, multiplier); err != nil {
 			return fmt.Errorf("disk space check failed: %w", err)
 		}
 
@@ -496,6 +527,9 @@ func runRestoreCluster(cmd *cobra.Command, args []string) error {
 		fmt.Printf("\nWould restore cluster:\n")
 		fmt.Printf("  Archive: %s\n", archivePath)
 		fmt.Printf("  Parallel Jobs: %d (0 = auto)\n", restoreJobs)
+		if restoreWorkdir != "" {
+			fmt.Printf("  Working Directory: %s (alternative extraction location)\n", restoreWorkdir)
+		}
 		fmt.Println("\nTo execute this restore, add --confirm flag")
 		return nil
 	}

internal/restore/safety.go

@@ -230,6 +230,11 @@ func containsSQLKeywords(content string) bool {
 
 // CheckDiskSpace verifies sufficient disk space for restore
 func (s *Safety) CheckDiskSpace(archivePath string, multiplier float64) error {
+	return s.CheckDiskSpaceAt(archivePath, s.cfg.BackupDir, multiplier)
+}
+
+// CheckDiskSpaceAt verifies sufficient disk space at a specific directory
+func (s *Safety) CheckDiskSpaceAt(archivePath string, checkDir string, multiplier float64) error {
 	// Get archive size
 	stat, err := os.Stat(archivePath)
 	if err != nil {
@@ -242,18 +247,33 @@ func (s *Safety) CheckDiskSpace(archivePath string, multiplier float64) error {
 	requiredSpace := int64(float64(archiveSize) * multiplier)
 
 	// Get available disk space
-	availableSpace, err := getDiskSpace(s.cfg.BackupDir)
+	availableSpace, err := getDiskSpace(checkDir)
 	if err != nil {
 		s.log.Warn("Cannot check disk space", "error", err)
 		return nil // Don't fail if we can't check
 	}
 
+	usagePercent := float64(availableSpace-requiredSpace) / float64(availableSpace) * 100
+	if usagePercent < 0 {
+		usagePercent = 100 + usagePercent // Show how much over we are
+	}
+
 	if availableSpace < requiredSpace {
-		return fmt.Errorf("insufficient disk space: need %s, have %s",
+		return fmt.Errorf("insufficient disk space for restore: %.1f%% used - need at least 4x archive size\\n"+
-			FormatBytes(requiredSpace), FormatBytes(availableSpace))
+			"  Required: %s\\n"+
+			"  Available: %s\\n"+
+			"  Archive: %s\\n"+
+			"  Check location: %s\\n\\n"+
+			"Tip: Use --workdir to specify extraction directory with more space (e.g., --workdir /u01/dba/restore_tmp)",
+			usagePercent,
+			FormatBytes(requiredSpace),
+			FormatBytes(availableSpace),
+			FormatBytes(archiveSize),
+			checkDir)
 	}
 
 	s.log.Info("Disk space check passed",
+		"location", checkDir,
 		"required", FormatBytes(requiredSpace),
 		"available", FormatBytes(availableSpace))