Choosing the hard drives…

Posted on April 22, 2011


Solving Life’s Storage Issues

The next important buying decision after choosing the NAS, is what hard drives to purchase. 

Hard drives are pretty standardized these days.  You basically have two sizes, laptop 2.5″ and desktop 3.5″  Fortunately the Synology DS411j can take both types, but best bang for the byte you’ll be looking at 3.5″ hard drives.  In a few years the super fast Flash Solid State SSD drives will be the standard NAS drive, but for now you’ll be looking at good old metal platters and magnets HDD (Hard Disk Drives).

Sticker Shock!

For most folks this often comes down to a budgetary issue, but that isn’t the only important thing to consider.   Hard drive stability, speed and capacity are all key elements in choosing appropriate drives for your NAS.

Just to set your expectation, it turns out that you will probably spend more on the hard drives for your NAS then you will have spent on the NAS itself!  In my case it was $360 for the NAS and $700 for hard drives!  Since this is the largest financial investment in your quest to build a NAS it is probably worthwhile to spend some time going over some basics.

To save money you might be tempted to scavenge from a collection of old hard drives you have laying around in underused computers and external hard drives to put in your NAS, but I’d advise against doing that.  You are likely to run into older drive connector problems (power & data cable) along with performance issues where the NAS has to compensate for the lowest common denominator of hard drive capacity and transfer speeds.

To save the environment you might be swayed to buy Green Power eco-friendly hard drives.  While the benefit of a drive that uses less power means a quieter drive (less noise, less heat for fans in the NAS to turn on) is appealing, the cost in performance is not.  Green drives get most of their power savings from lower RPM (rotation per minute) speed.  Most manufacturers don’t post the RPM speed on Green Drives, but I would always opt for the fastest hard drives (often called Blue drives) and use the Synology’s system scheduler to shut down the NAS during the hours when it is unlikely to be used if you really want to save on power usage.

The basic rules:

  1. Before you buy, PLEASE check Synology’s list of approved hard drives!  They do have a wiki site where end users can report if an untested drive worked for them, but if you’re smart you’ll buy from the approved list.  Approved drives support S.M.A.R.T. status and error reporting (like telling your NAS to turn on/off the fan, or if the drive is about to fail).  Your NAS is only as good as the HDDs in them.
  2. Fill all the drive slots with the same exact hard drive model.  You should get the maximum number of drives that the NAS will hold (most likely 2 or 4 depending on the model).  Only putting 2 drives in a 4 drive capable NAS will limit performance and backup options.  You are better off with four 1TB drives than two 2TB drives.  Upgrading smaller drives to larger drives later is possible and fairly straight forward.
  3. Buy 1 extra hard drive of the same exact kind as the ones you are putting in your NAS.  You can use this “spare” hard drive in your computer or keep it on a shelve, but you need to have it on hand in case a drive in your NAS starts to go bad.  Being able to replace a bad drive with the exact same model spare will ensure that the NAS can rebuild the missing drive with your spare.  This rebuild doesn’t always work when replacing with a different model of drive (trust me that 36 months from now your same hard drive model will no longer be sold).
  4. Do not buy 5400 rpm hard drives.  They would be useful if only 1 task is being requested from the NAS at a time.  Going with 7200 rpm drives allow multiple data requests to be handled with less likely hood that a data request for a realtime function (like watching video) would experience an interruption from another task like a Time Machine backup going at the same time.  The faster the drive spins the more data it can read and the more interruptions it can handle when having to jump across the platters to access multiple items at the “same” time (something SSD drives excel at).
  5. All drives should be in the internal drive bay slots.  Do not use the USB 2.0 connector to add external drives unless you are desperate to add drive space later to a NAS with no more internal slots.  USB 2.0 data transfer speed is actually slower than the internally connected NAS drives using gigabit data transfer over the ethernet to your PC so expect a slow down if you do this.
  6. Enterprise vs desktop.  The hard drives used in commercial data centers (Google, Facebook, Oracle, etc) are all enterprise rated drives.  These aren’t the drives you’ll find at a regular computer store, and they aren’t cheap.  If you are going to put a lot of demanding needs on your NAS you should look at these drives, but for the rest of us, saving money and limiting the abuse and heat we give our NAS will let you get away with using the much less expensive desktop class hard drives (just be sure to use a data backup system or RAID 1 or 5 configuration).

Hard drive sizing: 1TB, 2TB or 3TB drives for each slot?

Spend a few minutes to calculate your data needs.

Start with the existing content that you’ll be putting on the NAS.  This may include items like Time Machine backups, iTunes Media, photos, video, documents, etc.  In my case I was amazed that this represented almost 4TB of data.

You then need to factor in your future data storage needs.  Be sure to think about how much data you’ll be adding over the next 24-36 months.  Many folks think they can start with 1 hard drive now and keep adding drives as they need it.  This isn’t a great strategy.  Adding more hard drives to your NAS after the fact is possible, but your NAS will need to move a lot of data around in order to rebuild your drive setup, you’ll be limited by your previous RAID setup and if the drive sizes don’t match up you’ll be restricted by the size of the smallest drive.  Just formatting my 12TB setup (4x3TB) the first time took 23 hours of formatting and verifying by the Synology DS411j NAS.  This is not something I would want to go through again without just cause.

On top of what you need for data storage you need to add 25-50% for RAID 1 or 5 data protection.  If your NAS is simply a duplicate of existing data you could skip data protection and maximize your storage space, but over time the chance you’ll have a drive failure is almost assured.  Using RAID 1 on a 2 drive Synology NAS requires that 1 of the 2 drives is a mirror for the other drive (50%).  On a 4 drive Synology I would recommend Raid 5 (where any 1 drive failure could be automatically rebuilt by the remaining 3 drives) to help prevent a disaster in case of drive failure (25%).

Keep 10% reserved as free space (full hard drives suffer performance, fragmentation and stability issues).  This will help ensure you get the maximum performance out of your hard drives.

Remember that 7% of your hard drive’s capacity is used when formatting EACH hard drive.  It drives me nuts that manufacturers can advertise a drive’s storage size before formatting.  An unformatted  1TB hard drive only gives you 930GB of usable storage space.  Unformatted drive capacity (100%) vs formatted drive capacity (~93%).  A NAS with 4X1TB would have 3.7GB of available storage.

Sizing Formula: Data Needs (Backups, Media, Files, etc) + Future Needs + RAID Data Protection (25 or 50% of hard drive space) +10% Free Space +7% Formatting Loss per drive = Hard Drive Space You Need.

Buying Tips:

Some resellers do sell Synology units with the drives already installed but rest assured installing them yourself is very straight forward process involving a couple of screws and slide them in kind of install.

Heard bad things about 3TB drives?  The controversy over 3TB hard drives is related to the limitation Microsoft Windows PCs have with the Master Boot Record in BIOS.  This legacy issue means that Windows 7 64bit and earlier can’t use boot drives larger than 2.2TB,  but rest assured these 3TB drives will work just fine in your Synology.

In my case I decided to go with Hitachi’s 3TB “HDS723030ALA640” desktop drive from Synology’s approved list.  I ordered a total of 5 of these drives.  4 of them for the NAS, and one for use in my Mac Pro.  The reason for buying 5 is that if when one of the NAS drives fail I’ll have an identical backup drive that can be pressed into service.  This will help ensure that the data restore function on the NAS will work, as opposed to failing over drive differences in case this drive is no longer sold.

The biggest pain point in actually purchasing the hard drives  is that Synology lists the drive’s by the model number that is actually printed on the label found on the hard drive.  I’ve included a snapshot of my drive’s label to show you how much data is on here without any reference to the product’s actual name.  You can find the drive’s model number in the lower left corner – HDS723030ALA640.

When you go to Amazon or anyplace else and search on the model number you’ll get a listing of drive choices that don’t reference that number.  You can’t tell if it is an exact match, so you would be wise to google the model number and the manufacturer and confirm the full product name from the manufacturer’s product list.  In this case Hitachi model number: HDS723030ALA640 translates to: Hitachi Deskstar 3.5 inch 3TB 7200RPM SATA III 6Gbps 64MB Cache Internal Hard Drive.

Hard Drive Manufacturers

I’ve included the following information to help educate you on how few manufacturers there really are for all the hard drives sold on the market under various brand names.  I would encourage you to check out their support and warranty info before purchasing.

Western Digital is based in Southern California near Disneyland.  They are the largest hard drive manufacturer in the world with their recent acquisition of Hitachi’s hard drive business unit which had acquired IBM’s hard drive business unit that originally created the first hard drives in Silicon Valley back in 1953.

SeaGate Technology is based near Silicon Valley and named after its location off the highway that is Silicon Valley’s gateway to the sea.  SeaGate is the number two player in the market.  It acquired cross town rival Maxtor in 2006 and is rumored to be buying Samsung’s ailing hard drive business unit.

Toshiba based in Japan is the third largest manufacturer with it’s 2009 aquisition of Fujitsu.  They are the largest manufacturer of 2.5″ laptop hard drives.

Samsung based in Korea is in talks with SeaGate about acquiring their hard drive business to focus on making flash memory that is used in the new solid state drives(SSD).  Synology’s compatibility page makes several mentions of specific issues regarding Samsung hard drives so be sure to read the testing notes before buying.

HDD Trivia:

Synology DSM 3.1 uses Linux’s EXT4 file system formatting for hard drives.  EXT4 allows formatting of drives up to 1 EB (1 million TBs) in size and single files on the drive can be up to 16 TB in size.  Well beyond today’s current drive technology.

The History so far in Storage Sizes?

B – Byte, KB – KiloByte, MB – MegaByte, GB – GigaByte, TB – TerraByte

What’s Next in Storage Sizes?

PB – PetaByte, EB – ExaByte, ZB – ZettaByte, YB – YottaByte, BB – BrontoByte