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Re: Replace Disc ... SSHD

steveTu
Apprentice

Replace Disc ... SSHD

Model: ReadyNAS Duo [X-RAID] Serial: 24M3117Y01978 Firmware: RAIDiator 4.1.16 [1.00a043]  Memory: 256 MB [2.5-3-3-7]

 

Yesterday, the NAS booted on timer as usual but the power light went solid for a few seconds and then started to slowly flash with the disc 1 light flashing. The power and disc  lights then went off, and then came back again in slow flash mode. I couldn't get to Radiator to see any messages and I couldn't manually power down the device from the power button (it just recycled through the loop). I powered down by then removing the power cable, reseated the drives and rebooted with the same result. So I then tried removing a disc at a time and rebooting - and the device booted as soon as I removed drive 1. So it appears that drive 1 was dead or dying.

 

Anyway, the drive in the device is an old 2TB Seagate Barracuda ST2000DL003  5900 RPM - if I replace the drive can I put in a 2TB SSHD drive (Seagate ST2000DX002 FireCuda SSHD 2TB 7200rpm)? Any issues?

 

Message 1 of 9

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StephenB
Guru

Re: Replace Disc ... SSHD


@steveTu wrote:

Thanks - I appreciate and take on board your advice - but for future reference, can I ask what makes a drive more suitable for a NAS?


There are some drive firmware features (for instance TLER) that make a drive better suited for RAID.  TLER (Time Limited Error Recovery) is generally disabled on desktop class drives.  NAS purposed (and enterprise class) drives also are supposed to control vibration better, which is helpful in a larger NAS than the Duo.

 

Some larger drives (> 4 TB) use SMR technology, and doesn't work that well in a NAS.  Sustained write speeds with SMR are quite slow, which is a problem when the array is synced.  That's not an issue here though.

 

Generally Seagate and Western Digital don't recommend their desktop drives for RAID (other than RAID-1, which happens to be what your Duo is doing).

 

Note there are folks (for instance BackBlaze) who routinely use desktop-class drives in their RAID arrays anyway.  Though I think that is (at least in part) a risk/cost tradeoff that they are making (using a mix of cheaper drives, and risking replacing them more often).  

 

 

In this particular case, the Ironwolf is also a bit cheaper than the Barracuda.  Plus the Duo isn't really able to take advantage of the faster RPM, since it's performance is limited by it's CPU. You'll also be limited by the other old disk (like another 5900 rpm drive).  The large cache in the Barracuda (the SSHD) could be an advantage, though only if both drives in the array had it - and I don't think it would make much difference in practice, since the Duo is caching in it's RAM anyway.

 

FWIW, I use NAS-purposed drives in all my newer NAS (generally WD Reds, though I do have some IronWolf), and find they are cost-effective, quiet, reliable, power-efficient and give good performance.   My own Duo has an old Seagate Barracuda (ST32000542AS) and a newer WD Red (WD20EFRX) - no need to replace the Barracuda, as it is still working well.

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Message 4 of 9

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StephenB
Guru

Re: Replace Disc ... SSHD


@steveTu wrote:

 

Anyway, the drive in the device is an old 2TB Seagate Barracuda ST2000DL003  5900 RPM - if I replace the drive can I put in a 2TB SSHD drive (Seagate ST2000DX002 FireCuda SSHD 2TB 7200rpm)? Any issues?

 


Personally I'd get a NAS-purposed drive - WD Red or Seagate Ironwolf (ST2000VN004).  Though the FireCuda likely will work.

Message 2 of 9
steveTu
Apprentice

Re: Replace Disc ... SSHD

Thanks - I appreciate and take on board your advice - but for future reference, can I ask what makes a drive more suitable for a NAS?

Message 3 of 9
StephenB
Guru

Re: Replace Disc ... SSHD


@steveTu wrote:

Thanks - I appreciate and take on board your advice - but for future reference, can I ask what makes a drive more suitable for a NAS?


There are some drive firmware features (for instance TLER) that make a drive better suited for RAID.  TLER (Time Limited Error Recovery) is generally disabled on desktop class drives.  NAS purposed (and enterprise class) drives also are supposed to control vibration better, which is helpful in a larger NAS than the Duo.

 

Some larger drives (> 4 TB) use SMR technology, and doesn't work that well in a NAS.  Sustained write speeds with SMR are quite slow, which is a problem when the array is synced.  That's not an issue here though.

 

Generally Seagate and Western Digital don't recommend their desktop drives for RAID (other than RAID-1, which happens to be what your Duo is doing).

 

Note there are folks (for instance BackBlaze) who routinely use desktop-class drives in their RAID arrays anyway.  Though I think that is (at least in part) a risk/cost tradeoff that they are making (using a mix of cheaper drives, and risking replacing them more often).  

 

 

In this particular case, the Ironwolf is also a bit cheaper than the Barracuda.  Plus the Duo isn't really able to take advantage of the faster RPM, since it's performance is limited by it's CPU. You'll also be limited by the other old disk (like another 5900 rpm drive).  The large cache in the Barracuda (the SSHD) could be an advantage, though only if both drives in the array had it - and I don't think it would make much difference in practice, since the Duo is caching in it's RAM anyway.

 

FWIW, I use NAS-purposed drives in all my newer NAS (generally WD Reds, though I do have some IronWolf), and find they are cost-effective, quiet, reliable, power-efficient and give good performance.   My own Duo has an old Seagate Barracuda (ST32000542AS) and a newer WD Red (WD20EFRX) - no need to replace the Barracuda, as it is still working well.

Message 4 of 9
steveTu
Apprentice

Re: Replace Disc ... SSHD

@StephenB 

Thanks for that. I was thinking about replacing both drives - one immediately (obviously), and the other a bit later as I think I got the Duo about 9-10 years ago.

 

Thanks again.

Message 5 of 9
Sandshark
Sensei

Re: Replace Disc ... SSHD


@StephenB wrote:


Personally I'd get a NAS-purposed drive - WD Red or Seagate Ironwolf (ST2000VN004).  Though the FireCuda likely will work.


A bit off topic, but the latest WD Reds (WDxxEFAX) are SMR drives.  WD is very hush-hush on this.  It's unknown if they have a larger PMR section for temporary storage than their desktop counterparts.

Message 6 of 9
StephenB
Guru

Re: Replace Disc ... SSHD


@Sandshark wrote:

@StephenB wrote:


Personally I'd get a NAS-purposed drive - WD Red or Seagate Ironwolf (ST2000VN004).  Though the FireCuda likely will work.


A bit off topic, but the latest WD Reds (WDxxEFAX) are SMR drives.  WD is very hush-hush on this.  It's unknown if they have a larger PMR section for temporary storage than their desktop counterparts.


Interesting.  I'm seeing some posts out there on this, but nothing 100% certain.  Synology's Hard Drive HCL has an SMR note for the 2 TB and 6 TB drive, but not for the 8 TB and 10 TB models.  That's suspicious on it's face - there's no reason for anyone to build a 2 TB SMR drive.  Still it's odd that WD isn't talking - it's a pretty basic question.

 

FWIW I have a couple of EFAXs (two in my primary NAS), and haven't see any performance issues.

 

 

Message 7 of 9
Sandshark
Sensei

Re: Replace Disc ... SSHD

I now also have one 6TB EFAX drive combined with PMR drives and see no adverse effects on performance I can detect (and I tried).  I found the price of old stock EFRX drives astronomical and wondered why.  That's when I found the discussions that the AX are SMR.  I hold WD's refusal to refute the generally accepted "fact" to be a pretty good indication it's true.

 

As for no reason to produce a 2TB SMR drive, quantity of scale for anything common with the larger drives could be one.  Especially since the demand for smaller drives is likely to decrease, so doing something special for them becomes more expensive.

Message 8 of 9
StephenB
Guru

Re: Replace Disc ... SSHD


@Sandshark wrote:

 

As for no reason to produce a 2TB SMR drive, quantity of scale for anything common with the larger drives could be one.  


I'm not convinced on this point.  Unless they were forced to drop the old EFRX, it'd be simplest just to keep production going until HAMR/MAMR comes out at scale.  SMR would make more sense in the really large sizes, where WD is somewhat behind Seagate at the moment.

 

I do find this report interesting: https://www.theregister.co.uk/2019/03/07/hamr_and_mamr_hdd_direction_debate/  It indicates that WD has been looking closely at shingling, and that might not be only with MAMR.  Though normally you'd expect them to use it at the upper end of the capacity range - where they are somewhat behind Seagate at the moment.

 

FWIW, one rationale (aligned with your thinking) is that they are using 2 TB platters in the WD20EFAX and the WD60EFAX models.  https://rml527.blogspot.com/2010/10/hdd-platter-database-western-digital-35_9883.html  That of course would save cost, and it's possible that SMR might be needed to get the capacity with a single platter.

 

The lack of measured performance drops during extended writes (including resync) is interesting.  If that is really the case (as it seems), then they've come with with something to at least partially mitigate the main issue with SMR. 

 

One possibility that occurs to me (completely fabricated from thin air) is that perhaps 2 TB platter capacity wasn't quite acheivable with PMR.  The only way I know of to mitigate the performance drop is to increase the guard space between tracks periodically on the platter (creating "bands").  That reduces the extra density you get with SMR, but limits the write propagation.  If the 2 TB raw capacity was just a bit too low (say 5%), then they might be able to use small (closely spaced) bands - which would reduce the write propagation problem a lot.

 

 

 


@Sandshark wrote:

I now also have one 6TB EFAX drive combined with PMR drives and see no adverse effects on performance I can detect (and I tried).  I found the price of old stock EFRX drives astronomical and wondered why.  That's when I found the discussions that the AX are SMR.  I hold WD's refusal to refute the generally accepted "fact" to be a pretty good indication it's true.

I agree the refusal is odd (and it's not easy to find this out for Seagate models either).  

 

Though off-topic, WD launched their 4 TB NAS SSD last week.  Much more expensive than mechanical drives of course (~$600 MSRP), but significantly cheaper than the IronWolf 110 that was launched eariler this year.  Both WD and Seagate seem to be focused on NAS SSD caching, and not simply replacing mechanical disks with SSDs.

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