SANS DIGITAL Raid Tower Four Years On


Almost 4 years ago, I bought a Sans Digital MobileSTOR MS4UT+B four drive bay RAID tower.  Here’s how it’s stood up so far:

The reason I’m writing this article today, is because this past week was the first time one of my drives in the ARRAY failed.  To be clear, this is not a complaint.  ALL drives fail.  That’s WHY I bought a RAID tower, so that when one eventually DOES fail, I have the redundancy in place to keep going while I get a replacement drive, with zero down time and zero data loss.

Before reading further, if you don’t know what RAID is or a RAID tower, please click the link below for a straight-forward explanation:

When I bought the tower almost 4 years ago (this model is not available for sale anymore), I also bought 4 of these drives.  Click the image to see it on Amazon.

Seagate 4TB NAS HDD SATA 64MB Cache 3.5-Inch Internal Bare Drive (ST4000VN000)

for $149.99 each in December 2014.  They were the cheapest 4TB drives I could find at that time.

All 4 have been running 24/7 until 2018-10-29, when one of them finally failed.  To be honest, I expected the first failure to be years ago, considering my track record of at least 1 failed drive a year.  I bought the cheapest drives I could find too, so I expected more frequent failures.  The front panel of the RAID tower indicated that my drive #3 had died.

The computer was completely unaware of the failure.  This is a good thing.  That means the RAID tower’s seamless drive failure was working.  I immediately ordered a new, replacement drive.  I ordered the cheapest, 4TB drive I could find.  Why?  Because reliability of individual drives is not all that important when you have them in a RAID tower.  The redundancy of the whole system dramatically improves overall reliability, even when using low reliability drives.  I should also point out that just because a drive is inexpensive, doesn’t mean it’s also low reliability.

Here’s the drive I bought in late October 2018 for $79.99… nearly half the cost from 4 years earlier.  Click the image to see it on Amazon.

WL 4TB 7200RPM 64MB Cache SATA 6.0Gb/s 3.5″ Hard Drive (For RAID, NAS, DVR, Desktop PC) w/1 Year Warranty

What did I do?

When it arrived 3 days later, without shutting anything down, I opened the front panel of my RAID tower, pulled out the bad drive (with the whole system still on and running), unscrewed the 2 screws holding the handle onto the bad drive, screwed them and the handle onto the new drive, and plugged it into the RAID tower.

What did the RAID tower do?

The RAID tower immediately recognized the new drive and started replicating data to it.

What did the PC do?

My PC never knew anything ever happened.  As far as it was concerned, there was a working 12TB drive that it continued to actively use throughout the whole process.  There was never any downtime.

How long did it take?

Swapping the drive took about 5 minutes or less.  The replication, however, began on the night of Tuesday, October 30th.  It was still replicating when I left the PC on Saturday night, November 3rd.  However, Sunday morning, when I got back to it, it had finally finished.  So, it took it about FOUR DAYS to complete the replication.  Much longer than I thought.  I figured it would take between a couple hours up to maybe 1 day.

What does this mean?

It means that my data was vulnerable to disaster via a SECOND drive failure from the moment the drive went bad on Saturday, October 27th, through when the data was finally, fully replicated onto the new drive somewhere between the night of Saturday 11/3 and the morning of Sunday, 11/4… a total of a few hours more than 1 solid week.

If any other drive had died during that time, my 10TB of data would have been hosed.

The good news is that if I were NOT using a RAID tower, I’d be in that same risk ALL THE TIME!  I was only at risk for 7 days.  The BAD news (for YOU) if you’re not using RAID, you’re at that risk 100% of the time.


This RAID tower performed as designed and is still performing.  The vulnerable replication period is much longer than I expected.  But, in the end, it all worked.  This is the first drive failure I’ve had where I didn’t lose a single bit of data.

My recommendations:

Whether you need speed or reliability, you SHOULD be using a RAID array.  I highly recommend buying a RAID tower and let it handle the complexities of configuring the system.  Software RAID solutions are available, but they are much less reliable and consume resources on your computer, slowing you down.  With an external hardware solution, it’s literally just plug and play, like any normal, single external drive.  But with the capacity, speed, and reliability of a RAID solution.  RAID towers can be found for under $100 and there’s no upper limit to how much you can spend on one.


  1. Buy a RAID tower.
  2. Configure it to the configuration that best meets your needs.
  3. Have a local backup using a low cost, external USB hard drive of equal capacity as your full RAID array’s configuration.
  4. Have a cloud backup of your data too, AND MAKE DARN SURE IT’S ENCRYPTED ON YOUR END BEFORE BACKING UP!!!
    1. There are a lot of decentralized, peer-to-peer, cloud backup services coming online like:
      1. Sia
      2. FileCoin
      3. StorJ
      4. and others.  None of them are great solutions as of this writing YET!  But that’s changing.  Keep an eye on them and read EDUCATED reviews of them.  That includes keeping an eye on my blog because I’m watching them with intense interest, in addition to testing them myself.  I’ll ring the alarm bell when it’s time to jump on.  They WILL BE the ultimate backup solution.

What is RAID or a RAID tower?

RAID is an acronym that stands for “Redundant Array of Independent Disks”.  In short, it’s a system that allows you to make multiple hard drives look like a single drive to a computer that’s using them.  The benefits you get depend on the RAID configuration you choose and the hardware and/or software you use to implement RAID.  Your RAID configuration options are:

RAID Towers

RAID 0:  Striping.  This treats all the platters in all your drives in the RAID 0 configuration as one drive with multiple platters.  On a regular, single drive system, a hard drive usually has multiple, physical disks inside of it.  Data is written on the disks on tracks, similar to a record player, but unlike a record player that has ONE groove that spirals all the way from the outer edge to the center, computer disks have individual rings, called “tracks”.  A hard drive has multiple disks (called “platters”), each with tracks.  A file is written across the multiple platters on the same track until that track, on all the platters, is full, then another empty space is found to continue the writing.  With RAID 0, you can add more drives to extend the depth of those tracks. One file is now written across all platters on all drives on the same track until they’re filled.  There’s no limit to how many drives you can have in a RAID 0 configuration (except limits imposed on your RAID hardware and/or software).

Benefits of RAID 0:

  • Speed
  • Larger volume size.

Disadvantages of RAID 0:

  • Decreased reliability.  If any one drive fails, the whole thing goes down.  The more drives you have in a RAID 0 configuration, the sooner the whole thing will die or the LESS fault tolerant it is.  RAID 0 is pretty dangerous and should not be used unless speed is more important than reliability.

RAID 1:   Mirroring.   Given X amount of drives in ANY RAID configuration, you can have a duplicate copy of them, which requires twice as many drives.  All drives have to be the same capacity.  Neither set is the “original”.  All data written to one set is duplicated on the other.  Both sets are live.  For example:  The simplest RAID 0 configuration is a 2 drive system, both drives of equal size each.  Your total storage capacity across the system is exactly the capacity of ONE of those drives.  Everything written to one drive is duplicated on the other.  A more complex RAID 0 configuration will more more than 2 drives, but ALWAYS an even number of drives.  The 1st half of drives can be any other RAID configuration you like.  The 2nd half of drives will be a duplicate of the same thing.

Benefits of RAID 1:

  • 100% redundancy.  Acts as a full, live backup.  Any part of either side can fail and the array continues to function, seamlessly.
  • Speed.  Mirroring doesn’t require extra processing.  It’s no slower than a single drive with no RAID.

Disadvantages of RAID 1

  • Capacity is reduced to 1/2 the total capacity of the whole, physical system.

RAID 3:  RAID 3 is made of exactly 3 drives.  2 drives for data, one for parity.  Any 1 drive can fail and the system can continue to function until you replace the bad drive, in which case, the new drive is restored from the remaining 2 drives.

Benefits of RAID 3:

  • Redundancy
  • Capacity.  Maximum capacity usage for data across your array of disks.

Disadvantages of RAID 3:

  • Speed.  RAID 3 requires extra processing and thus, results in somewhat slower performance.
RAID Towers

RAID 5: RAID 5 is nearly identical to RAID 3, with the added benefit that you can use any number of drives you like.  You’re not limited to 3.  Instead of dedicating drives to data or parity, every drive in a RAID 5 configuration contains BOTH data AND parity.  2/3 of every drive contains data and 2/3 of every drive contains parity.

Benefits of RAID 5:

  • Same as RAID 3 plus…
  • Not limited to 3 drives.  Can have 2 or more, with no practical limitation.

Combining RAID configurations: It should be noted that you can combine RAID 1 with any of the other configurations.  A popular configuration is stripping (RAID 0) plus mirroring (RAID 1), known as any of the following labels:

  • RAID 0+1
  • RAID 1+0
  • RAID 10

Benefits of combining stripping and mirroring:

  • Maximum Speed
  • Maximum Redundancy & reliability


  • The same disadvantage of mirroring:  Your total capacity of all your drives is cut in half.

What is a RAID Tower, then?

A RAID tower is a piece of hardware with multiple drive bays.  You can plug in your own hard drives in the tower.  The tower usually has the hardware and software built in to handle the RAID configurations for you.  You plug the tower into a computer and it appears simply as a single, external disk drive with the full capacity of whatever RAID configuration you assigned the drive array.

RAID is a concept.  A RAID tower is a functioning product implementing that concept.

A special note about RAID and SSDs (Solid State Drives)

SSDs, as you probably know, are the modern replacements for the decades old, spinning disks we call “hard drives”.  SSDs have no moving parts and are 100% solid state electronics.  They’re essentially memory chips that don’t lose their data when you turn them off, making them ideal for a modern replacement for hard drives.  Because they have no moving parts, they’re significantly faster and more reliable.  They’re also a lot more expensive (for now) per gigabyte of storage.

Can RAID work with SSDs?

Yes!  In fact, my personal desktop PC is using two 256GB SSDs in a RAID 0 configuration.  Why RAID 0, when it’s known to be less reliable?  for several reasons:

  1. Speed.  Yes, even though SSDs are significantly faster than spinning platters with moving read/write robotic arms, they can be even faster in a RAID 0 configuration.
  2. Reliability:  No, I’m not using RAID 0 to make them more reliable.  They are, in fact, LESS reliable in a RAID 0 configuration, but since they’re SSDs, even with two of them in a RAID 0 configuration, they’re still more reliable than a single, spinning disk drive.
  3. I need speed more than reliability on my boot drive.  Why?  All my important data is stored on my RAID tower.  Everything on my boot drive can be restored by simply re-installing all of my software.  The only thing I’ll lose is my time.

Actually, the primary reason is I’d purchased a 256GB SSD for another computer and didn’t need it in that one anymore and I wanted 512GB SSD for my desktop, so I just bought a second 256GB drive and put them both in, configured as a RAID 0 system.  I’m perfectly fine with it for the reasons listed above.

But, enough about me.  Yes, SSDs can be used in any RAID configuration that spinning platter disk drives can be with the same pros and cons.  It’s just that every configuration on an SSD is faster than the same configuration on spinny disks (as I like to call them).  Also, every option is more expensive with SSD.