I recently suffered one of those storage network failures that you have nightmares about.  After spending more than $1000 on a NetGear ReadyNAS NV+, I had a catastrophic failure that cost me all of the data on the system.  Believe it or not, it was a single drive failure – exactly the type of problem you spend money on a RAID system to survive.  Unfortunately, in my case, it didn’t.

On the bright side, I had the opportunity to rethink and rebuilt my storage and backup solutions from scratch.  In a recent blog post, I described my new network and storage topology.

Synology DS1511+ to the Rescue

The Synology DS1511+ is a great device.  It sits on your Gigabit network, handles up to five SATA hard drives, and can act as a wide variety of servers for your network.  I configured my with five 3TB Western Digital Caviar Green drives, for 15TB of notional storage, 8.3TB of usable storage.

The Synology supports “dual drive redundancy”, so for the price of 2 drives worth of storage, you end up with protection for your data even if two drives fail simultaneously.  Needless to say, I went for that option.

The industrial design of the box is well done.  You do have to break out the screwdriver to install the drives into trays (not quite as nice as the Drobo FS plug-and-play SATA drives), but the case itself is small, quiet and black.  It also has nice locks on each drive bay, which has made it “child proof” for my 2 year old who is unfortunately fascinated with the blinking lights.

The Synology box is incredibly fast.  First, it supports two Gigabit Ethernet ports, to establish connections from multiple clients independently.  But even from one machine, it’s wicked fast.  Simple Finder copy of a 500MB file to the drive takes under 6 seconds.  I was able to back up 2.7M files totally 4.05TB in size using Time Machine (usually dog slow) in about 26 hours.

The Synology management software is Windows 2000 like in terms of its user interface and incredible breadth of options.  Needless to say, I only use about 1% of them.  I did run into one issue, and hence the title of this blog post.  Configuring the box for Time Machine on Mac OS X 10.7 Lion was non-trivial.

Time Machine on Mac OS X 10.7 Lion & Synology DSM 3.2

Time Machine, unfortunately, is the most consumer friendly solution for incremental backup on the Mac.  Unfortunately, if you have multiple machines, you run into a small issue: Apple designed the software as if it “owns” the entire drive you point it at.  As a result, you can’t just point all your machines at a single network drive without a number of bad things happening.

Instead, you have to somehow convince Time Machine to only use part of the drive.  This turned out to be quite an issue for me, since I wanted to be able to backup my machine (~4TB) as well as my wife’s MacBook Pro (~500GB).

Synology has published documents on how to configure the box for Time Machine, and has designed it’s software around a very clever option.  The basic idea is that you create a different “user” for each machine you want to back up with Time Machine.  For each user, you assign a limited quota, and then you tell Time Machine to use that user for the Synology volume.  It actually works quite well, although it feels a little strange to create separate user accounts for each machine, on top of accounts for each user.

The Undocumented 4TB Limit

Unfortunately, I ran into an undocumented issue.  When I tried to set the quota for my machine to 6000 GB (in general, you want to give 50% extra room for incremental changes / backups), Time Machine would only see about 1.8 TB.  When I checked the DSM 3.2 interface, I found indeed that it had reset 6000 GB to 1804 GB.  After trying to set it several times with the same issue, I deduced that the maximum limit was 4096 GB, and that it was “wrapping” around that number.  Sure enough, entering 4100 -> 4, and entering 4096 actually turned to 0, shutting off the quota entirely!

After some back and forth with Synology customer service, they finally admitted this was true.  (The first two times, they claimed that the issue was with Mac OS X 10.7 Time Machine not respecting quotas.)  I hope they fix the software to at least tell the user when they type a number over 4095 that they’ve exceeded the limit.

The Solution: Disk Groups, Volumes & Shares

To solve the problem, I reverted to a more old-fashioned solution: partitions.  Of course, with a sophisticated, modern RAID box, this was a bit more complex.  The Synology DSM 3.2 software supports three relevant concepts:

• Disk Groups:  You can take any number of the drives and “bind” them together as a disk group.
• Volumes:  You can allocate an independent “volume” of any size over a disk group.
• Shares:  You can specify a share on a given volume which is available to only certain users.

The key here is that normally you use quotas to limit storage on shares for specific users.  But since I was looking for a “6 TB” share, there was no way to do this.  By default, shares get access to the entire volume they are on, so the key was to repartition the box into separate volumes.

As a result, I configured my box as follows:

• One disk group across all 5 disks, configured for dual drive redundancy using Synology Hybrid Raid (SHR)
• Three volumes: one for my iMac’s time machine (6000 GB), one for my wife’s Macbook Pro (1000 GB), and one remainder for network storage (1.3 TB)
• For each volume, I configured a single share, without quota limits.  I gave my account access to my backup share, my wife her backup share, and gave everyone access to the general media share

Works like a charm.  My iMac sees the 6TB volume for Time Machine, mounts it as needed, and backs up every hour.  Thanks to the incredible Synology speed, most incremental backups happen in the background in seconds without any noticeable performance lag.  In fact, the original backup of 4.05TB with Time Machine took about 26 hours.  On my NetGear ReadyNAS NV+, that same initial backup took almost a week.

Recommendation: Synology DS1511+

I have to just say that, despite some back and forth over the Time Machine issue, the Synology website, wiki and documentation are all well done.  They are clearly responsive, even responding to my issues over Twitter.  Given the industrial design, features, and performance of the box, I have no trouble recommending the DS1511+ to anyone who’s looking for a large (10TB+) network attached storage solution for backup of a mixed network.

Disclosure: Synology was kind enough to provide me the DS1511+ free of charge given my difficult situation.