Non Enterprise Drive

[titusc]

Hi, given QNAP uses Linux software RAID, will the QNAP series of NASes drop a disk out from the array if it's trying to recover from a bad sector and taking its time (ie more than 10 seconds)? Since with enterprise drives it has TLER it'd opt to indicate a block as unrecoverable and let the RAID to recover it from the other disks, the cheaper non enterprise drives don't have this feature and will keep trying for a long time (ie exceeding 10 seconds if required). Would this cause a problem with QNAP's NASes?

I'm going to be using RAID 1 only. Can't bother with RAID 5 as I'm only after redundancy.

BTW can I have 4 drives all in RAID 1?

[pwilson]

Hi, given QNAP uses Linux software RAID, will the QNAP series of NASes drop a disk out from the array if it's trying to recover from a bad sector and taking its time (ie more than 10 seconds)? Since with enterprise drives it has TLER it'd opt to indicate a block as unrecoverable and let the RAID to recover it from the other disks, the cheaper non enterprise drives don't have this feature and will keep trying for a long time (ie exceeding 10 seconds if required). Would this cause a problem with QNAP's NASes?

I'm going to be using RAID 1 only. Can't bother with RAID 5 as I'm only after redundancy.

BTW can I have 4 drives all in RAID 1?

For 4 Drives, you are probably looking for RAID10, which is simply a RAID0 striped arrray, of 2 RAID1 mirrored arrays of 2-drives each.

Check out the: Volume Management section of the: QNAP Turbo NAS Software User Manual

[titusc]

Thanks but I'm looking for all disks in the array containing the same information. Is this possible? All 3 or 4 drives have identical content?

[pwilson]

Thanks but I'm looking for all disks in the array containing the same information. Is this possible? All 3 or 4 drives have identical content?

You said you were interested in RAID1, so I thought that was what you were looking for.
I personally stick with RAID5 on my 4-Bay NAS (TS-419P+).



This provides redundancy by the use of "parity", and I only loose 25% of my diskspace in order to provide this redundancy.
Works like a champ. I have already survived a hard disk failure under RAID5, and I lost no data whatsoever. I simply replaced the defective drive, and allowed the NAS to re-build the RAID5 array with the new drive installed. It worked like a champ.

[P3R]

Thanks but I'm looking for all disks in the array containing the same information. Is this possible? All 3 or 4 drives have identical content?

Not possible as far as I know. A 3-disk RAID 6 offer the same redundancy as a 3-disk RAID 1 would. A hot spare could be added for the highest supported disk redundancy in a 4-bay model.

When in need of extreme redundancy, you probably also should consider other things than disk redundancy. Of course a quality UPS is a must and there are Qnap models with redundant power supplies (RP-models).

You could also use RTRR in realtime mode to get system redundancy. Switch over would not be fully automatic but with intelligent management the change could be made simple for users. I think dual synchronized RAID 1-servers would beat a 4-disk RAID 1 for availability.

[titusc]

Not possible as far as I know. A 3-disk RAID 6 offer the same redundancy as a 3-disk RAID 1 would. A hot spare could be added for the highest supported disk redundancy in a 4-bay model.

Think you meant "... 3-disk RAID 5" there.
RAID 1 requires minimum 2 disks and can survive 1 disks outage.
RAID 5 requires minimum 3 disks and can survive 1 disk outage.
RAID 6 requires minimum 4 disks and can survive 2 disks outage.

The issue comes with the re-silvering operation scare given the high URE to TB ratio. Shouldn't be a factor if we're talking about only four 1TB disks. However, given it will become a risk with the multiple 3TB disks setup with not being able to recover from 1 disk failure due to URE, I try to stay away from RAID 5 or 6 from the onset.

Also, if the option of having 3 disks all containing the exact replica in a RAID 1 setup, I only need to buy 3 disks and can loose up to 2 disks. This is in comparison of using 3 disks in a RAID 5 setup and only able to loose 1 disk. Besides from an IO perspective, write speed for RAID 1 will be quicker than RAID 5 since it doesn't have to calculate parity.

Anyway back to the original question. Are we able to use non enterprise disks in these NASes? If they are using software Linux RAID, are these NASes going to drop a drive out of the array if a non enterprise disk is trying to recover from a bad block for an extended period of time (ie over 10s)?

[P3R]

RAID 6 requires minimum 4 disks and can survive 2 disks outage.

Sorry about that. Since the configuration you want isn't supported I was trying to be creative but forgot about the requirement to have at least 4 disks in RAID 6.

The issue comes with the re-silvering operation scare given the high URE to TB ratio.

Ahh, the old URE-myth. Okay, let's deal with that again.

According to the myth, RAID 5 should have stopped working with 2 TB disks in 2009. Well we all know that didn't happen. The prediction made above is based on the specified guaranteed number of bits read (usually 1 in 10^14 for desktop disks) before suffering from a URE, but disks generally perform much, much better than the absolute minimum specified.

Of course the theory is valid in the respect that with larger disks, a URE is more likely to happen during a rebuild. The problem with the theory is that a single figure (with questionable validity) on a datasheet can't be used as the sole basis for such an analysis. The risk for a URE happening during a RAID rebuild shouldn't be neglected, it is real and can happen but taking desperate measures (like a 4 disk RAID 1) to avoid it is in my opinion a huge overreaction. To begin with, this is one of the many dangers that backups will protect you from.

Disk fault tolerance isn't meant to secure the data from disasters, that is what backups are for. Disk redundancy is only there to improve uptime and make the path back to a normal system status easier when the inevitable disk failures does happen.

Shouldn't be a factor if we're talking about only four 1TB disks.

2 TB desktop disks have been used in RAID 5 and RAID 6 for many years now. Since about 18 months there must be several thousand of arrays running with 3 TB desktop disks and I haven't noticed any alarming increase of failed rebuilds. I don't expect it to become terrible with 4 TB disks either.

Also, if the option of having 3 disks all containing the exact replica in a RAID 1 setup, I only need to buy 3 disks and can loose up to 2 disks. This is in comparison of using 3 disks in a RAID 5 setup and only able to loose 1 disk.

Well the comparison isn't really fair. I guess you intend to have the disks to store data and then you must be aiming for some storage volume. Considering the configuration you talk about I guess it is 3 TB? With a RAID 5 you could use 4*1 TB disks to get to that same number and suddenly we're back at your trusted 1 TB disks. With RAID 6 you could use 4 of the very well proven 2 TB disks to get 4 TB storage and have the same 2 disk redundancy as in your 3*3 TB RAID 1, all for less money!

If you consider the write performance hit of RAID 6 too big then RAID 10 is the alternative (with a slightly lower redundancy but better performance than RAID 1).

Besides from an IO perspective, write speed for RAID 1 will be quicker than RAID 5 since it doesn't have to calculate parity.

True, but read speeds will be better for RAID 5 because of the striping. It's of course a matter of personal preference which is most important.

Are we able to use non enterprise disks in these NASes?

Yes.

If they are using software Linux RAID...

They are.

...are these NASes going to drop a drive out of the array if a non enterprise disk is trying to recover from a bad block for an extended period of time (ie over 10s)?

It depends on how long the disk is trying to recover but I can't give you any specific numbers because I don't know the exact timeouts. I only know that many, including myself, are running RAID 5 with desktop disks and it works well.

In fact I'm pretty sure a large majority of Qnap-users does use desktop disks. Especially Hitachi and Samsung have received much praise by forum users since several years back.

However, be very careful about what specific disks you choose. Look at the Qnap disk compatibility list and also search the forum for customer experiences. All WD Caviar Green is of course out of the question. Personally I would avoid all WD desktop disks and all of the very new Seagate desktop models (except the rebranded Samsungs).

[titusc]

Thanks after doing some research, I believe I'll choose the following setup.
TS-459 PRO + (for some reason it's cheaper than the TS-439 PRO II + despite the 459 is a dual core and the 439 isn't.
RAID 6 (since I can get 4 x 500GB drive for an effective 1TB useable space and still able to loose up to 2 disks).

Now the question is which disk to choose. After searching online for prices based on disks from the 3.5" compatibility list, I have narrowed to the following.
Hitachi HDS723015BLA642 1.5TB 7k SATA III Consumer $555
Hitachi HDT721010SLA360 1.0TB 7k SATA II Consumer $420
Seagate ST3500320NS 0.5TB 7k SATA II Enterprise $590

It appears the Seagate one is quite cheap for an Enterprise drive but am thinking of just going for the Hitachi 1.0TB one because of the following.
Seagate disks are problematic (at least based on what we see on this forum).
Enterprise feature such as TLER isn't useable by Linux RAID and even if the the NAS does drop it from the RAID twice I still have two disks left in my RAID 6.

Sounds like a good plan?

[P3R]

Seagate disks are problematic (at least based on what we see on this forum).

As far as I know the Seagate compatibility problems are limited to some newer desktop models. Apart from the WD RE4-GP (it may not not be a coincidence that it doesn't seem to be available any more), I haven't noticed many problems reported by Qnap-customers here in the forum with any enterprise disk from any manufacturer.

Enterprise disks, including the Seagate Barracuda ES.2 above, does offer a specification claiming at least 1 in 10^15 bits read until a URE happens. That's 10 times more than the desktop Hitachi disks.

[titusc]

Hi, just dropped to a retail shop but was told the HDT721010SLA360 and HDS723015BLA642 are legacy models and currently they only have HDS721010DLE630 on market as listed on the following page:
http://www.hgst.com/deskstar-7k1000d

Also trying to search for Seagate's ST3500320NS online it's no where to be found on their official home page list of their Constellation drives. This is a bit concerning.
http://www.seagate.com/internal-hard-dr ... lation-es/

Ignoring the Seagate for the moment, I am currently stuck in not knowing which drive to choose. This is becasue the HDS721010DLE630 despite as being new it isn't listed on the compatibility page. Any idea if HDS721010DLE630 would work with the TS-459 PRO +?

[P3R]

Hi, just dropped to a retail shop but was told the HDT721010SLA360 and HDS723015BLA642 are legacy models and currently they only have HDS721010DLE630 on market as listed on the following page:
http://www.hgst.com/deskstar-7k1000d

Yes i was a bit confused about that you had prices on those older models..

Also trying to search for Seagate's ST3500320NS online it's no where to be found on their official home page list of their Constellation drives.

Well that's because it isn't a Constellation model. If you google it you'll notice that it is a now phased out Barracuda ES.2 model. It's still an enterprise disk but again I was surprised to see you presenting a price on it. This is documentation on the disk, that appeared on my first google page.

Ignoring the Seagate for the moment, I am currently stuck in not knowing which drive to choose. This is becasue the HDS721010DLE630 despite as being new it isn't listed on the compatibility page.

Generally I would imagine any new compatibility testing is concentrated on the currently best selling models and that is most likely 2 TB disks and higher today.

Any idea if HDS721010DLE630 would work with the TS-459 PRO +?

The HDS721010DLE630 is probably an older model that have just been updated with a new interface. It's not likely, but unfortunately that change may make it incompatible. My guess would be that you're on your own trying it out.

[titusc]

The HDS721010DLE630 does work with the TS-459 PRO +.