diff --git a/scst/include/scst.h b/scst/include/scst.h
index dc2551bbf..6b01af6b6 100644
--- a/scst/include/scst.h
+++ b/scst/include/scst.h
@@ -33,6 +33,8 @@
 #ifdef CONFIG_SCST_PROC
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
+#elif defined(RHEL_MAJOR) && RHEL_MAJOR -0 <= 5
+#error The SCST sysfs interface is not supported on RHEL 5. Please run 'make enable_proc'.
 #endif
 
 #include <scsi/scsi_cmnd.h>
@@ -122,7 +124,7 @@ static inline void cpumask_copy(cpumask_t *dstp,
 }
 #endif
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 26)
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 26) && !defined(RHEL_MAJOR)
 static inline int set_cpus_allowed_ptr(struct task_struct *p,
 				       const cpumask_t *new_mask)
 {
diff --git a/scst/src/dev_handlers/scst_vdisk.c b/scst/src/dev_handlers/scst_vdisk.c
index 5cc83de9c..12c795c39 100644
--- a/scst/src/dev_handlers/scst_vdisk.c
+++ b/scst/src/dev_handlers/scst_vdisk.c
@@ -1353,7 +1353,9 @@ static void vdisk_exec_unmap(struct scst_cmd *cmd, struct scst_vdisk_thr *thr)
 	}
 
 	while ((offset - 8) < descriptor_len) {
+#if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 27)
 		int err;
+#endif
 		uint64_t start;
 		uint32_t len;
 		start = be64_to_cpu(get_unaligned((__be64 *)&address[offset]));
@@ -1566,7 +1568,7 @@ static void vdisk_exec_inquiry(struct scst_cmd *cmd)
 			put_unaligned(cpu_to_be32(max_transfer),
 					(uint32_t *)&buf[8]);
 			/*
-			 * Let's have optimal transfer len 1MB. Better to not
+			 * Let's have optimal transfer len 512KB. Better to not
 			 * set it at all, because we don't have such limit,
 			 * but some initiators may not understand that (?).
 			 * From other side, too big transfers  are not optimal,
@@ -1574,15 +1576,18 @@ static void vdisk_exec_inquiry(struct scst_cmd *cmd)
 			 */
 			put_unaligned(cpu_to_be32(min_t(int,
 					max_transfer,
-					1*1024*1024 / virt_dev->block_size)),
+					512*1024 / virt_dev->block_size)),
 				      (uint32_t *)&buf[12]);
 			if (virt_dev->thin_provisioned) {
 				/* MAXIMUM UNMAP LBA COUNT is UNLIMITED */
-				put_unaligned(cpu_to_be32(0xFFFFFFFF),
-					      (uint16_t *)&buf[20]);
+				put_unaligned(__constant_cpu_to_be32(0xFFFFFFFF),
+					      (uint32_t *)&buf[20]);
 				/* MAXIMUM UNMAP BLOCK DESCRIPTOR COUNT is UNLIMITED */
-				put_unaligned(cpu_to_be32(0xFFFFFFFF),
-					      (uint16_t *)&buf[24]);
+				put_unaligned(__constant_cpu_to_be32(0xFFFFFFFF),
+					      (uint32_t *)&buf[24]);
+				/* OPTIMAL UNMAP GRANULARITY is 1 */
+				put_unaligned(__constant_cpu_to_be32(1),
+					      (uint32_t *)&buf[28]);
 			}
 			resp_len = buf[3] + 4;
 		} else if ((0xB2 == cmd->cdb[2]) &&
diff --git a/scst/src/scst_main.c b/scst/src/scst_main.c
index 6479639bc..f994ff42e 100644
--- a/scst/src/scst_main.c
+++ b/scst/src/scst_main.c
@@ -1575,8 +1575,13 @@ int scst_add_threads(struct scst_cmd_threads *cmd_threads,
 			strlcpy(nm, tgt_dev->dev->virt_name, ARRAY_SIZE(nm));
 			thr->cmd_thread = kthread_create(scst_cmd_thread,
 				cmd_threads, "%s%d_%d", nm, tgt_dev_num, n++);
+#ifdef RHEL_MAJOR
+			rc = set_cpus_allowed(thr->cmd_thread,
+				tgt_dev->sess->acg->acg_cpu_mask);
+#else
 			rc = set_cpus_allowed_ptr(thr->cmd_thread,
 				&tgt_dev->sess->acg->acg_cpu_mask);
+#endif
 			if (rc != 0)
 				PRINT_ERROR("Setting CPU affinity failed: "
 					"%d", rc);