Protection - more
I would like to see the NSA-2400 be able to back up to another brand of NAS. As mentioned above, the included Genie software allows desktop backups to other NAS devices, but ZyXEL doesn't include that functionality in the NSA-2400. If my network were graduating from a small NAS to a storage device like the NSA-2400, it would be attractive if I could still get some value out of my small NAS device in a backup role.
The Snapshot functionality is based on the Linux Enterprise Volume Management System (EVMS). There is a good user guide for EVMS technology located at SourceForge here. The NSA-2400 Snapshot functionality uses disk space on the NSA-2400 to make copies of the changed data on an entire volume.
The NSA defaults to reserving 30% of the total available disk space for snapshot storage. The amount of space reserved for snapshots can be configured to be more or less than the default value of 30%, but once configured, can't be increased. A guide to determining the appropriate amount of snapshot space is to consider the usage of the volume. A network volume with a lot of activity will likely need more snapshot space than a lightly used volume.
Creating a snapshot is straightforward. Simply click Add a New Snapshot Job, select which volume you want to make snapshots of, and optionally enter a description of the job. Once the job is created, you can click a little camera icon meaning Execute Job Now, or you can use the Scheduler.
The Scheduler tool automates NSA Backup and Snapshot jobs. As you can see in Figure 12, jobs can be scheduled to run daily, weekly, or monthly. The nice thing about the Scheduler is it runs on the NSA-2400 independent of any software installed on a PC or Server.
Figure 12: The Scheduler tool
RAID and Disk Management
ZyXEL’s product web page states that the NSA-2400 supports JBOD, RAID 0, 1 and 5. It is interesting that a manufacturer would underreport their product capability, as the NSA-2400 has choices to configure disk arrays with JBOD, RAID 0, RAID 1, RAID 5, RAID 5_SPARE, and RAID 10. Apparently, ZyXEL enhanced the NSA's capability without updating the website or marketing material.
The RAID 5_SPARE is an interesting option. This option results in a three-disk RAID 5 array with the fourth disk in standby mode. If one of the three disks fails, the NSA will automatically resynchronize the array using the fourth disk. (For more details about RAID arrays, check out Tim Higgins’ article here.)
Depending on the number of disks you have, you can create various data volumes of various types. Keep in mind, though, that adding or replacing disks on the NSA-2400 requires a system shutdown. The NSA supports disk "quick swap," but does not support hot swappable disks. Figure 13 is a matrix of the formatting options available.
Figure 13: Matrix showing disk volume options
For example, with two disks, you could create one to two JBOD volumes, OR one RAID 0 or RAID 1 volume. With three disks, you could create one JBOD volume PLUS one RAID 0 or RAID 1 volume. With four disks, you could create multiple different volumes, depending on your storage needs.
I tried several different configurations, using ZyXEL’s Disk Setup wizard and default options to create the array. (4) 250GB hard drives configured in a single JBOD volume resulted in a 652GB volume with 279GB of snapshot space. The RAID 5 option resulted in a 489GB volume with 209GB of snapshot space. The RAID 5_SPARE option resulted in a 465GB volume with 139GB of snapshot space. Selecting the RAID 10 option resulted in just a 326GB volume with 139GB of snapshot space.
Once you choose your disk configuration and acknowledge that you are aware it will result in losing all data on the volume by formatting your disks, you are presented with a system busy screen, Figure 14, while the NSA-2400 prepares your configuration. Note that configuration options in the Sharing, Network, Protect, and Maintenance window were not erased by the formatting process.
Figure 14: System busy while formatting drives
Although the above message for creating a new volume states it only takes a few minutes, there is a lot of activity going on in the background for quite a bit longer. To create a RAID 1, RAID 5, or RAID 10 array, the NSA-2400 needs to synchronize the volume across the selected drives. Synchronizing a RAID 10 array took 196 minutes.
The system is functional while the NSA is synchronizing, yet the manual recommends against accessing or saving data during this process. A look at the Status screen while synchronization is underway showed the NSA's CPU fluctuating, at times up to 100%, resulting in sluggishness of the web admin screens. Drive failure during synchronization would likely result in extensive to total data loss, so it makes sense to complete this activity before putting your NSA into production, or during the maintenance window.