Summary: The Synology DS 1515+ is a capable little NAS with a large feature set, but it has some software reliability issues and limited technical support.
The DS1515+ is a compact unit that feels sturdy. It holds five 2.5″ or 3.5″ drives, and 3.5″ drives can be installed without any tools. You will need a Phillips-head screwdriver to install an additional RAM module, but that’s also a very simple process. The fans are also easily replaceable.
You will need to connect the DiskStation to the Internet to install the operating system, which is called DiskStation Manager (DSM). The installation process went smoothly. From a security standpoint, this process is slightly scary, and I hope that the automated installation process used some method to verify the integrity of the operating system.
Once the operating system is installed, there is a nice graphical user interface to manage all aspects of the system. It is possible to enable SSH to allow access to the unit by command line, but the CLI is officially undocumented, and Synology support won’t answer questions about it. The documentation on the Synology support site is pretty thorough, so I won’t go through the process to create a RAID or volumes.
Every feature on this NAS introduces a potential security hole. Be sure that every sharing feature is disabled, unless you specifically intend to use it. Enable the firewall, and block access to all ports and services by default. Then, go back and enable the specific services that you need. Also, install the advanced log manager application from Synology (I don’t know why it doesn’t come pre-installed).
I purchased two units and created a High Availability (HA) configuration. I will clarify a few points regarding the HA configuration. Each unit has 4 1Gb Ethernet ports. One of those ports on each unit should be DIRECTLY connected to the other unit (not through a switch). This link is used to synchronize the two units. The other three ports may be used for external connectivity. Also, be sure that RAIDs and network interfaces have identical configurations on each unit prior to activating the HA cluster. Once HA is activated, you will not be able to change these settings on the secondary unit. This is mostly a concern if you set up the cluster in a “lab” environment that requires a different network setup than your “production” environment.
I configured this NAS cluster to serve as both an office shared drive and as a storage pool for virtual machines. I assigned an IP address on the office subnet to one Ethernet interface, and activated the Windows file sharing service on this interface. The single interface provided sufficient bandwidth for sharing typical office files, such as MS Office documents. One of the reasons we selected this NAS is because it advertised Active Directory (AD) integration. However, AD authentication of shared volumes became a major source of problems. Several times per week, the NAS suddenly refused to authenticate new shared drive connections. Users who had already mapped a drive were able to access files, but no new users could mount shared drives from Windows PCs. The resolution seemed completely random; sometimes, re-joining the domain was sufficient to re-enable share authentication. Other times, I spent a frantic 30 minutes randomly restarting services until it started working again.
Synology support was frustrating; it took 24-48 hours to receive a response from a Level 1 support person. After about two weeks of back-and-forth, our case was finally escalated to engineers in Taiwan. Interaction with the engineers was even slower due to the time difference. I still do not know what finally solved the problem. We added the IP addresses of both domain controllers to the DNS settings as a comma-separated list, and we updated DSM to version 6.0.2-8451-3. We also gave the engineers SSH access to the NAS, and maybe they changed something. Windows file sharing has been operating reliably for over a month now, but I am slightly hesitant to update DSM again.
Virtual Machine Storage
I bonded the two remaining Ethernet interfaces and assigned an address on an infrastructure subnet. This bonded interface was connected to two small “virtual host” servers running CentOS 7 and KVM/QEMU/libvirt. I created an NFS share on the DS to store VM images, and mounted the NFS share on each Linux host. We experimented with iSCSI, but found that VMs actually booted more slowly when booting from an iSCSI target. Further, iSCSI is more difficult to manage, since each iSCSI target maps to exactly one virtual drive. If you need to add space to a VM, you have to log into the DiskStation and create additional targets. With NFS, the DS provides a large storage pool, and all VM disks can be managed on the servers.
Performance hosting VMs is generally adequate. I encountered problems when taking “snapshots” of VMs and copying them to another network share for backup purposes. Prior to DSM 6.0.2-8451-3, the nightly snapshot operation would frequently fail, and I would have to do it manually. I found that copying more than one VM image (typically 40 to 60GB) at a time was a recipe for trouble. The network would effectively lock up while the images copied. Since other VMs couldn’t access their disks, they would also freeze until the copy operation completed.
The DS has the ability to monitor a UPS and automatically go into “safe mode” when low battery is detected. Unfortunately, only a few UPS models are supported, and most of them are from Synology. This is a major limitation when the NAS is used to store virtual machines; if the NAS shuts down prior to the virtual hosts, the VMs will just lose their disks, and experience an unclean shutdown.
In some ways, the Synology DS1515+ is a pretty amazing value. For about $700-750 retail (without drives), you get a lot of enterprise-grade features, such as RAID 6, four GigE interfaces, high-availability clustering, SNMP monitoring, syslog sending and receiving, and the ability to run apps on the DiskStation. I plan to try some of the apps that sync files from the DS to cloud services like Google Drive, DropBox, and so on. However, when it comes to reliability and support, you get what you pay for. TrueNAS from iX Systems is a more expensive solution, but support comes with a Service Level Agreement, and their engineers are located in the United States.
Performance was adequate and reliability was good when serving as a SAN to store virtual machines; a SAN should be based on 10GigE, Fibre Channel, or Infiniband network. The inability to control shutdown in the event of a power failure is a serious limitation.
Performance was good when serving as an office shared drive, but the reliability issues and reluctant support make me hesitate to recommend this unit for mission-critical applications.