18TB Home NAS/HTPC with ZFS on Linux (Part 1)

I have recently built a home NAS / HTPC rig. Here is my experience from research, building it, and experimentation, for the interested in building a similar solution or to improve upon it… or just for the curious. I ended up including more details and writing longer than I first planned, but I guess you can skip over the familiar parts. I’d certainly have appreciated reading a similar review or write up while shopping and researching.

6x 3TB WD RED drives cut from the same stock.

I have included a number of benchmarks to give actual performance numbers. But first, the goals:

Purpose: RAID array with >= 8TiB usable space, to double as media server.

Cost: Minimum with highest data-security.

Performance requirements: Low write loads (backups, downloads, camera dumps etc.), many reads >= 100mbps with 2-3 clients.

TL;DR: ZFS on Linux, powered by AMD A8 APU, 2x4GB RAM and 2x16GB flash drive in Raid-1 boot drive, backed by 6x3TB WD Red in Raidz2 (Raid-6 equivalent) for under $1400 inc. tax + shipping. The setup was the cheapest that met or exceeded my goals and is very stable and performing. AMD’s APUs are very powerful for ZFS and transcoding video, RAM is sufficient for this array size and flash drives are more than adequate for booting purposes (with the caveat of low reliability in the long-run). ZFS is a very stable and powerful FS with advanced and modern features at the cost of learning to self-serve. The build gives 10.7TiB of usable space with double-parity and transparent compression and deduplication, with ample power to transcode video, at a TCO of under $125 / TiB (~2x raw disk cost). Reads/Writes are sustained above 350MB/s with gzip-9 but without deduplication.

This is significantly cheaper than ready NAS solutions, even when ignoring all the advantages of ZFS and generic Linux running on a modern quad core APU (compare with Atom or Celeron that often plague home NAS solution).

Research on hardware vs. software RAID

The largest cost of a NAS are the drives. Unless one wants to spend an arm and a leg on h/w raid cards, that is. Regardless, the drives were my first decision point. Raid-5 gives 1 disk redundancy, but due to high resilver time (rebuilding a degraded array) chances of secondary failure increase substantially during the days and sometimes weeks that resilvering takes. Drive failures aren’t random or independent occurrences, as drives from the same batch, used in the same array, tend to have very similar wear and failure reasons. As such, Raid-5 was not good enough for my purposes (high data-security). Raid-6 gives 2 drive redundancy, but requires a minimum of 5 drives to make it worthwhile. With 4 drives, 2 used for parity, Raid-6 is about as good as a mirror. Mirrors however have the disadvantage of being susceptible to failure if the 2 drives that fail happen to be the same on both sides of the mirror. Raid-6 is immune to this, but IO performance is significantly poorer than mirroring.

Resilver time could be reduced significantly with true h/w raid cards. However they cost upwards of $300 for the cheapest and realistically $600-700 for the better ones. In addition, most give peak performance with backup battery, which costs more and will need some maintenance I expect. At this point I started comparing h/w with s/w performance. My personal experience with software data processing told me that a machine that isn’t under high-load, or is dedicated for storage, should do at least as good as, if not better than, the raid card’s on-board processor. After all, the cheapest CPUs are much more powerful, have ample fast cache and with system RAM that is in the GBs running at least at 1333 Mhz, they should beat h/w raid easily. The main advantage of h/w raid is that, with the backup battery, it can flush cached data to disk even on power failure. But this assumes that the drives still have power! For a storage box, everything is powered from the same source. So the same UPS that will keep the drives spinning will also keep the CPU and RAM pumping data long enough to flush the cache to disk. (This is true provided no new data is being written when on battery power.) The trouble with software raid is that there is no abstraction of the disks to the OS, so it’s much harder to maintain (the admin will maintain the raid in software). Also, resilvering with h/w will probably be lighter on the system as the card will handle the IO without affecting the rest of the system. But, I was to accept the performance penalty I was probably going to meet my goals even during resilvering. So I decided to go with software Raid.

The best software solutions were the following: Linux Raid using MD, BtrFS or ZFS. The first is limited to traditional Raid-5 and Raid-6 and is straightforward to use, is bootable and well-supported, but it lacks any modern features like deduplication, compression, encryption or snapshots. BtrFS and ZFS have these features, but are more complicated to administer. Also, BtrFS is still not production-ready, unlike ZFS. So ZFS it was. Great feedback online on ZFS too. One important note on software raid is that they don’t play well with h/w raid cards. So if there is a raid controller between the drives and the system, it should be set to bypass the devices or work in JBOD mode. I’ll have more to say on ZFS in subsequent posts.

To reach 8TiB with 2 drive redundancy I had to either go with 4x4TB drives or 5x3TB. But with ZFS (RaidZ) growing the array is impossible. The only solutions are to either add larger drives (one at a time and resilver until all have larger capacity and then the new space becomes available to the pool,) or, to create a new vdev with a new set of drives and extend the pool. While simply adding a 6^th drive to the 5 existing would have been a sweet deal, when the time comes I could upgrade all drives with larger one and enjoy new drive longevity and extra disk space. But first I had to have some headroom, so it was either 5x4TB = 12TB or 6x3TB=12TB.

Which drives? The storage market is still recovering from the Thailand flood. Prices are coming down, but they are still not great. The cheapest 3TB are very affordable, but they are 7200 rpm. Heat, noise and power bill are all high with 6 drives in an enclosure. They also come with 1 year warranty! Greens are cool and low on power requirements, but they are more expensive. The warranty isn’t much better, if at all longer. WD Red drives cost ~$20 more than the greens, come with all the advantages of 5400 rpm drive, are designed for 24/7 operation and have 3 year warranty. The only disadvantage of 5400 rpm drives is lower IOPS. But 7200 rpm doesn’t make a night-and-day difference anyway. Considering that it’s more likely than not that more than 1 drive will fail during 3 years, the $20 premium is a warranty purchase if not for the advantage of NAS drive vs. home usage. There was no 4 TB Red to consider at the time (Seagate and WD have “SE” 4TB drives that cost substantially more), although the cost per GB would be the same, it was outside my budget (~$800 for the drives) and I didn’t have immediate use for 16TB space of usable to justify the extra cost.

Computer hardware

AMD’s APU with its tiny heatsink and 2x 4GB DIMMs. Noticeable is the absence of a GPU (which is on the CPU chip).

I wanted to buy the cheapest hardware I could buy to do the job. I needed no monitor, just an enclosure with motherboard, ram and cpu. The PSU had to be solid to supply clean, stable power to the 6 drives. Rosewill’s Capstone is one of the best on the market at a very good price. The 450W version delivers continuous 450W power, not peak (which is probably in the ~600W range). I only needed ~260W continuous plus headroom for initial spin up. The case had to be big enough for the 6 drives + front fans for keeping the already cool-running drives even cooler (drive temperature is very important for data integrity and drive longevity). Motherboards with > 6 SATA ports are fewer and typically cost significantly more than with 6 or less. With 6 drives in raid, I was missing a boot drive. I searched high and low for a PCI-e SSD, but it seems there was nothing on offer for a good price, not even used ones (even the smallest ones were very expensive). Best price was for WD Blue 250GB (platter) for ~$40, but that was precious port that it would take, or cost me more in motherboard with 7 SATA ports. My solution was to use a flash drive. They are SSD and they come in all sizes and at all prices. I got two A-DATA 16GB drives for $16 each, thinking I’d keep the second one for personal use. It was after I placed the order that I thought I should RAID-1 the two drives to get better reliability.

With ZFS, RAM is a must, especially for deduplication (if desired). It is recommended to have 1-2GB for each TB of storage. So far, I see ~145 bytes / block used on core (RAM) which for ~1.3TiB of user data in 10million blocks = 1382MB of RAM. Those 10million blocks were used by <50K files (yes, mostly documentaries and movies at this point). The per-block requirement goes down with increased duplicate blocks, so it’s important to know how much duplication there are in those 1.3TiB. In this particular case, almost none (there were <70K duplicate bocks in those 10million). So if this was all the data I had, I should disable dedup and save myself RAM and processing time. But I still have ~5TiB of data to load with all of my backups, which sure have a metric ton of dups in them. Bottom line: 1GB of ram per 1TiB of data is a good rule of thumb, but it looks like it’s a worse-case scenario here (and that would leave little room for file caching). So I’m happy to report that my 8GB ram will do OK all the way to 8TiB of user data and realistically much more as I certainly have duplicates (yes, had to go for 8GB as budget and RAM price hike of 40-45% this year alone didn’t help. Had downwards price trends continued from last year, I should have gotten 16GB for almost the same dough). Updates on RAM and performance below.

CPU wise, nothing could beat AMD APU, which includes Radeon GPU, in terms of price/performance ratio. I could either go for dual core at $65 or quad core for $100 and upgrade L2 cache from 1MB to 4MB and better GPU core. I went for the latter to future proof video decoding and transcoding and give ZFS ample cycles for compression, checksum, hashing and deduplication. The GPU in the CPU also loves high-clock RAM. After shopping for a good pair of RAMs that work in dual-pump @ 1600Mhz, I found 1866Mhz ones for $5 more that is reported to clock to over 2000Mhz. So G.Skill wins the day yet again for me as is the case on my bigger machine with 4x8GB @ 1866 G.Skill. I should add that my first choice in both cases had been Corsair as I’ve been a fan for over a decade. But at least on my big build they failed me as they weren’t really quad-pump (certainly not at the reported frequency and G.Skill has overclocked to 2040Mhz from 1866Mhz while the CPU is at 4.6Ghz, but that the big boy, not this NAS/HTPC).

Putting it all together

I got the drives for $150 each and the PC cost me about $350. Two 16GB USB3.0 flash drives are partitioned for swap and rootfs. Swap is on Raid-0, ext4 on Raid-1. Even though I can boot off of ZFS, I didn’t want to install the system on the raid array, in case I need to recover it. It also simplifies things. The flash drives are for booting, really. /home, /usr, and /var should go on ZFS. I can backup everything to other machines and all I’d need is to dd the flash drive image onto a spare one to boot that machine in case of a catastrophic OS failure. Also, I keep a Linux Rescue disk on another flash drive at hand at all times. The rescue disk automatically detects MD partitions and will load mdadm and let me resilver a broken mirror. One good note is to set mdadm to boot in degraded mode and rebuild or send an email to get your attention. You probably don’t want to go in with a rescue disk and a blank screen to resilver the boot raid.

The 6 Red drives run very quietly and are just warmer than the case metal (when ambient is ~22C), enough that they don’t feel metallic-cold at sustained writing thanks to two 120mm fans blowing on them. Besides that, no other fans are used. AMD comes with an unassuming little cooler that is less loud than my 5 year old laptop. A-Data in raid gives upwards of 80MB of sustained reads (average over full drive dd read) and drop to ~19MB of sustained write speed. Bursts can reach 280MB/s and writes a little over 100MB/s. Ubuntu Minimal 13.04 was used (which comes with Kernel 3.8) and kernel upgraded to 3.11, ZFS 28 (the latest available for Linux, Solaris is at 32, which has transparent encryption) installed and 16.2TiB of raw disk space reported after Raidz-2 zpool creation and 10.7TiB of usable space (excluding parity). The system boots faster than the monitor (a Philips 32” TV) turns on (that is to say in a few seconds). The box is connected with a Cat-5 to the router, which has a static IP assigned to it (just for my sanity).

I experimented with ZFS for over a day just to learn to navigate it while reading on it before scratching the pool for the final build. Most info online are out of date (from 2009 when deduplication was all the rage in FS circles) so care must be taken when reading about ZFS. Checking out the code, building and browsing it certainly helps. For example, online articles will tell you Fletcher4 is the default checksum (it is not) and that one should use it if they want to improve dedup performance (instead of the much slower sha256), but the code will reveal that deduplication is defaulted and forced to sha256 checksum and that is the default even for on-disk checksums for integrity checks. Therefore, switching to Fletcher4 will only increase the risk of on-disk integrity checking, without affecting deduplication at all (Fletcher4 was removed from the dedup code when a severe bug was found due to endianness). The speed should only be worse with Fletcher4 if dedup is enabled because now both checksums must be done (without dedup Fletcher4 should improve the performance at the cost of data security as Fletcher4 is known to have a much higher collision rate than sha256).

ZFS administration is reasonably easy and it does all the mounting transparently for you. It also has smb/nsf sharing administration built-in, as well as quotas and acl support. You can set up as many filesystems as necessary anywhere you like. Each filesystem looks like a folder with subfolders (the difference between the root of a filesystem within another or just a plain subfolder is not obvious). The advantage is that each filesystem has its own settings (which are inherited from the parent by default) and statistics (except for dedup stats, which are pool-wide). Raid performance was very good. Didn’t do extensive tests, but sustained reads reached 120MB/s. Ingesting data from 3 external drives connected over USB 2.0 is running at 100GB/hour using rsync. Each drive is writing into a different filesystem on the same zpool. One is copying RAW/Jpg/Tif images (7-8MB each) on gzip-9 and two copying compressed Video (~1-8GB) and SHN/FLAC/APE audio (~20-50MB) on gzip-7. Deduplication is enabled. Checksum is SHA256. ZFS has background integrity check and auto-rebuild of any corrupted data on disk which does have a non-negligible impact on the write rates as the Red drives could do no more than ~50 random read IOPS and ~110 random write IOPS, but for the aforementioned load each levels at ~400 IOPS per drive since most writes are sequential. These numbers fluctuate with smaller files such that the IOPS drops down to 200-250 per drive and average ingestion is 1/3^rd at ~36GB/hour. This is mostly due to the FS overhead on reads and writes that force much higher seek rates vs sequential writes. CPU is doing ~15-20% user and ~50% kernel, leaving ~25% idle on each of the 4 cores at peak times and drops substantially otherwise. Reading iostats show about 30MB/s sustained reading rate from the source drives combined and writes on the Reds that average 50MB/s but spike at 90-120MB/s (this includes parity which is 50% of the data and updates of FS structure, checksums etc.)

2x 16GB flash drives in RAID-1 as boot drive and HDMI connection.

UPDATE: Since I wrote the above, it’s been 3 days. I now have over 2TiB of data ingested (I started fresh after the first 1.3TiB). The drives sustain at a very stable ~6000KB/s writes and anywhere between 200 and 500 IOPS (depending on how sequential they are). Typically it’s ~400 IOPS and ~5800KB/s. This translates into ~125GiB/hour (about 85GiB/hour of user data ingestion), including parity and FS overhead. Even though with gzip-9 and highly compressible data the rate or writing goes down, I now am writing from 4 threads and the drives are saturated at the aforementioned rates. So at this point I’m fairly confident the bottleneck of ingestion are the drives. Still, 85GiB/hour is decent for the price tag. I haven’t done any explicit performance tests because that was never in my goals. I’m curious to see the raw read/write performance, but this isn’t a raw Raid setup, so the filesystem overhead is always in the equation and that will be very much variable as data fills up and dedup tables grow. So the numbers wouldn’t be representative. Still, I do plan to do some tests when I ingest my data and have a real-life system with actual data.

Regarding compression, high-compression settings affect only performance. If the data is not compressible, the original data is stored as-is and no penalty for reading it is inured (I read the code,) nor is there extra overhead in storage (incompressible data typically grows a bit when compressed). So for archival purposes the penalty is slower ingestion speed. Unless modification will happen, slow and good compression is a good compromise as it does yield a few % points compression even on mp3 and jpg files.

With Plex Media Server installed on Linux, I could stream full HD movies over WiFi (thanks to my Asus dual-band router) transparently while ingesting data. Haven’t tried heavy transcoding (say HD to iphone) nor have I installed windows manager on Linux (AMD APUs show up in forums with Linux driver issues, but that’s mostly old and for 3D games etc.) Regarding the overhead of dedup, I can disable dedup per filesystem and remove the overhead for folders that don’t benefit anyway. So it’s very important to design the hierarchy correctly and have filesystems around file types. Worst case scenario: upgrade to 16GB RAM, which is the limit for this motherboard (I didn’t feel the need to pay an upfront premium for a 32GB max MB).

I haven’t planned a UPS. Some are religious about availability and avoiding hard power cuts. I’m more concerned about the environmental impact of batteries than anything else. ZFS is very resilient to hard reboots, not least thanks to its journaling and data checksums and background scrubbing (validating checksums and rebuilding transparently). I had two hard recycles that recovered transparently. I also know ztest which is a dev test tool does all sorts of crazy corruptions and kills and it’s reported that in 1million tests no corruptions were found.

Conclusion

For perhaps anything but the smallest NAS solutions, a custom build will be cheaper and more versatile. The cost is the lack of warranties of satisfaction (responsibility is on you) and the possibility of ending up with something underpowered or worse. Maintenance might be an issue as well, but from what I gather ready NAS solutions are known to be very problematic, especially when they show any issues, like failed drive or buggy firmware or management software. ZFS proved, so far at least, to be fantastic! Especially that deduplication and compression really work well and increase the data density without compromising integrity. I also plan to make good use of snapshots, which can be configured to auto-snapshot with a preset interval, for backups and code. I only miss transparent encryption from ZFS on Linux (Solaris got it, but it hasn’t been allowed to trickle down yet.) Otherwise, I couldn’t be more satisfied (except may be with 16GB RAM, or larger drives… but I would settle for 16GB RAM for sure.)

Parts

PCPartPicker part list: http://pcpartpicker.com/p/1GqNv
Price breakdown by merchant: http://pcpartpicker.com/p/1GqNv/by_merchant/
Benchmarks: http://pcpartpicker.com/p/1GqNv/benchmarks/

CPU: AMD A8-5600K 3.6GHz Quad-Core Processor ($99.99 @ Newegg)
Motherboard: MSI FM2-A75MA-E35 Micro ATX FM2 Motherboard ($59.99 @ Newegg)
Memory: G.Skill Sniper Series 8GB (2 x 4GB) DDR3-1866 Memory ($82.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Storage: Western Digital Red 3TB 3.5″ 5400RPM Internal Hard Drive ($134.99 @ Newegg)
Case: Cooler Master HAF 912 ATX Mid Tower Case ($59.99 @ Newegg)
Power Supply: Rosewill Capstone 450W 80 PLUS Gold Certified ATX12V / EPS12V Power Supply ($49.99 @ Newegg)
Other: ADATA Value-Driven S102 Pro Effortless Upgrade 16GB USB 3.0 Flash Drive (Gray) Model AS102P-16G-RGY
Other: ADATA Value-Driven S102 Pro Effortless Upgrade 16GB USB 3.0 Flash Drive
Total: $1147.89
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-22 12:33 EDT-0400)