fix: restrict SinglePool by the minimum free drive threshold (minio#21115)

Author: jiuker

cmd/erasure-server-pool.go

@@ -635,15 +635,18 @@ func (z *erasureServerPools) getPoolIdxNoLock(ctx context.Context, bucket, objec
 // if none are found falls back to most available space pool, this function is
 // designed to be only used by PutObject, CopyObject (newObject creation) and NewMultipartUpload.
 func (z *erasureServerPools) getPoolIdx(ctx context.Context, bucket, object string, size int64) (idx int, err error) {
-	idx, err = z.getPoolIdxExistingWithOpts(ctx, bucket, object, ObjectOptions{
+	pinfo, _, err := z.getPoolInfoExistingWithOpts(ctx, bucket, object, ObjectOptions{
 		SkipDecommissioned: true,
 		SkipRebalancing:    true,
 	})
+
 	if err != nil && !isErrObjectNotFound(err) {
-		return idx, err
+		return -1, err
 	}
 
-	if isErrObjectNotFound(err) {
+	idx = pinfo.Index
+	if isErrObjectNotFound(err) || pinfo.Err == nil {
+		// will generate a temp object
 		idx = z.getAvailablePoolIdx(ctx, bucket, object, size)
 		if idx < 0 {
 			return -1, toObjectErr(errDiskFull)
@@ -1089,6 +1092,10 @@ func (z *erasureServerPools) PutObject(ctx context.Context, bucket string, objec
 
 	object = encodeDirObject(object)
 	if z.SinglePool() {
+		_, err := z.getPoolIdx(ctx, bucket, object, data.Size())
+		if err != nil {
+			return ObjectInfo{}, err
+		}
 		return z.serverPools[0].PutObject(ctx, bucket, object, data, opts)
 	}
 
@@ -1816,6 +1823,10 @@ func (z *erasureServerPools) PutObjectPart(ctx context.Context, bucket, object,
 	}
 
 	if z.SinglePool() {
+		_, err := z.getPoolIdx(ctx, bucket, object, data.Size())
+		if err != nil {
+			return PartInfo{}, err
+		}
 		return z.serverPools[0].PutObjectPart(ctx, bucket, object, uploadID, partID, data, opts)
 	}