2 drives NAS - fundamentally wrong concept?

[Vlad]

Is 2 drives NAS concept fundamentally wrong? Single drive NAS relies on one hard disk to be healthy. 3+ drives use one of RAID levels tolerating one or more drives failure or data corruption. 2 drives concept is based on incorrect assumption that SMART and/or NAS is capable to detect every disk data corruption or failure.

2 drives NAS is even less reliable than 1 drive NAS, as it needs two healthy disks to operate error free. If one drive in 2 drives NAS corrupts data, and the failure is by its nature not detectable by SMART, data integrity is lost; it is not possible to prevent copying corrupted data across disks.

In summary we have the following situation:

• 1 drive: no protection against data corruption
• 2 drives: as above, but reliability is decreased, both disks need to be healthy
• 3 and more drives: depending on RAID level and how many drives, protects against data corruption on one or more disks

.

 

[stevech]

Is 2 drives NAS concept fundamentally wrong? Single drive NAS relies on one hard disk to be healthy. 3+ drives use one of RAID levels tolerating one or more drives failure or data corruption. 2 drives concept is based on incorrect assumption that SMART and/or NAS is capable to detect every disk data corruption or failure.

2 drives NAS is even less reliable than 1 drive NAS, as it needs two healthy disks to operate error free. If one drive in 2 drives NAS corrupts data, and the failure is by its nature not detectable by SMART, data integrity is lost; it is not possible to prevent copying corrupted data across disks.

In summary we have the following situation:

• 1 drive: no protection against data corruption
• 2 drives: as above, but reliability is decreased, both disks need to be healthy
• 3 and more drives: depending on RAID level and how many drives, protects against data corruption on one or more disks

.

Not in my opinion. If you are assuming RAID1 or mirroring, where if one drive becomes corrupt, that gets replicated to the mirror drive - is the way 2 drive NASes are always used.

I use mine as two independent volumes. Independent file systems. Most but not all folders/files on one are synch'd to the other once a day (could be more frequently). And one volume has a time backup of the other drive's key folders - so the last 90 days of file versions are there - to protect from human error (e.g., I bonked that file in error).

And so on.

and my daily auto-backup of most folders/files to an external USB3 drive that's not in sight, is help in anti-theft.
Plus use of a large capacity SD card in the NAS to backup VVIP files.

My last 5 years' experience tell me that the most risk to data loss is not drive failure. With BIG NASes and SANs, with high drive counts, the statistics change.

And too, file system corruption, common 5-10 years ago due to unsophisticated file systems, is very rare today.

 

[Vlad]

You are correct.

However I was not really referring to using 2 drives NAS as two independent volumes. What you describe is conceptually the same as using two 1 drive NAS-es, a multiple disks NAS in a non-RAID configuration, or even a set of external, single drives which are not NASes. If one is not concerned with hard drive failure the whole concept of RAID is rather questionable.

Perhaps for clarity better title would be: "Is using 2 drives NAS configured as a RAID fundamentally wrong concept?"

 

[stevech]

You are correct.

However I was not really referring to using 2 drives NAS as two independent volumes. What you describe is conceptually the same as using two 1 drive NAS-es, a multiple disks NAS in a non-RAID configuration, or even a set of external, single drives which are not NASes. If one is not concerned with hard drive failure the whole concept of RAID is rather questionable.

Perhaps for clarity better title would be: "Is using 2 drives NAS configured as a RAID fundamentally wrong concept?"

On the last sentence: I'd say that RAID1/mirroring is not prudent today, as the likelihood of data loss in a small NAS is more human error, theft, NAS mainboard or power supply failure (which are the key causes of a RAID to garbage both drives at once).

 

[TonyH]

HI,
IMO, main purpose of using RAID is i/o speed I believe. No matter how big a RAID system it needs a back up. It's like firing a machine gun vs. rifle.

 

[Vlad]

HI,
IMO, main purpose of using RAID is i/o speed I believe. No matter how big a RAID system it needs a back up. It's like firing a machine gun vs. rifle.

This actually is a very complex subject. In short: it depends what data, and what RAID configuration. There are many scenarios when RAID slows things down. Google it if you are curious, but the only single and straightforward answer is... it depends.

 

[L&LD]

3 and more drives: depending on RAID level and how many drives, protects against data corruption on one or more disks

This doesn't protect against data corruption either. RAID5 and it's many variants simply tries to reduce the risk of mechanical drive failures. It too knows nothing about data corruption (on its own).

 

[stevech]

This doesn't protect against data corruption either. RAID5 and it's many variants simply tries to reduce the risk of mechanical drive failures. It too knows nothing about data corruption (on its own).

Nor does RAID protect from human error (oops, I deleted that; oops, I saved a honked up version of that document, etc. That's why time backup (as QNAP/Synoology have), reduce lost time and money.

My observation is that most NAS calamities are power supply or mainboard failures that corrupt both/all drives in the RAID array, or do so during an attempt to rebuild. That and other reasons lead to "RAID is not a backup".

 

[cone_head]

My thoughts on the term ’NAS’ or Network attached STORAGE does not include any type of redundancy or data security, it’s all about space.

Whether it’s a single drive, two drive or 50 drives, when I see or use the term NAS its all bout space.

The two drive concept is not wrong when used with the term NAS.
To me then term NAS only entails one thing….SPACE, nothing more, nothing less.

John-Q-Public’s typical intended use will be for media or satiating ones desire to save anything and everything. Their last thought is about drive failure and incremental backups or proper RAID set up.

When data retention and security is serious then your also going to be serous on how you go about it be it at the home or office and taking the NAS to the next level.

 

[Kris404]

My thoughts on the term ’NAS’ or Network attached STORAGE does not include any type of redundancy or data security, it’s all about space.
..

I think you mean the usecase for NAS as a cheap storage mechanism not necessarily the concept of NAS itself.

NAS has many other usecases including mission critical ones in Enterprises for things such as Vmware, Hyper-V (via NetApp, EMC VNXe, Isilon etc).

For a home usecase, if data redundancy is not such a priority and require less overhead to maintain, then a device such as Apple TimeCapsule would suit you just fine instead of building your own.

 

[Cloud200]

Is 2 drives NAS concept fundamentally wrong? Single drive NAS relies on one hard disk to be healthy. 3+ drives use one of RAID levels tolerating one or more drives failure or data corruption. 2 drives concept is based on incorrect assumption that SMART and/or NAS is capable to detect every disk data corruption or failure.

2 drives NAS is even less reliable than 1 drive NAS, as it needs two healthy disks to operate error free. If one drive in 2 drives NAS corrupts data, and the failure is by its nature not detectable by SMART, data integrity is lost; it is not possible to prevent copying corrupted data across disks.

In summary we have the following situation:

• 1 drive: no protection against data corruption
• 2 drives: as above, but reliability is decreased, both disks need to be healthy
• 3 and more drives: depending on RAID level and how many drives, protects against data corruption on one or more disks

.

By your analysis the following must be true;

1 drive JBOD has greater reliability than 2 drive RAID 1.
thus 2 drive RAID 1 has greater reliability than 3 drive RAID 6.
and may heaven help you if you dare use more than 4 drives in an array.

While the prior statements are absolutely true, you neglect to recall the most important fact of all. RAID IS NOT A BACKUP.
it is for one of three things;
1. speed
2. space
3. tolerance to mechanical failures

Now if you check real world practice, I have seen far less catastrophic failures with RAID arrays vs JBOD just because you don't lose all your data when a drive suffers a head crash.

Let me ask you a thought problem then;
what is more reliable?
2 drives in a 2 bay NAS set up in JBOD.
or
4 drives in a 4 bay NAS set up with 2 RAID 1 arrays.

now for both devices do the following;
Make it so the primary has a one way RSYNC from the other with automatic deletion retention for 90 days.

By your logic the first would be more reliable but I would bet my money on the second.