raid levels and NAS drives

raid levels and NAS drives

[Charles Zeitler]

Is there any advantage to using NAS drives
under RAID levels,  as oppposed to regular
'desktop' drives for BTRFS?

Charles Zeitler

-- 
 The Perfect Is The Enemy Of
 The Good Enough

Re: raid levels and NAS drives

[Tomasz Kusmierz]

And what exactly are NAS drives ?

Are you talking marketing by any chance ? Please, tell me you got the pun.

On 10 October 2016 at 00:12, Charles Zeitler <cfzeitler@gmail.com> wrote:
> Is there any advantage to using NAS drives
> under RAID levels,  as oppposed to regular
> 'desktop' drives for BTRFS?
>
> Charles Zeitler
>
> --
>  The Perfect Is The Enemy Of
>  The Good Enough
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
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Re: raid levels and NAS drives

[Tomasz Kusmierz]

On 10 October 2016 at 02:01, ronnie sahlberg <ronniesahlberg@gmail.com> wrote:
> (without html this time.)
>
> Nas drives are more expensive but also more durable than the normal consumer
> drives, but not as durable as enterprise drives.
> They are meant for near continous use, compared to consumer/backup drives
> that are meant for only occasional use and meant to spend the majority of
> time spinned down.
>
>
> They fall in-between consumer and enterprise gear.
>

Again, you read a marketing flyer ...

Historically enterprise drives did equal to a drive with SCSI, after
that it started to equal to a drive with more exotic interfaces like
SAS or FATA ... nowadays this means more in line "high [seak]
performance, for which you pay extra extra extra buck" (10k, 15k
arrays of 10 disks with databases on it that are serving plenty of
people ?).
Currently, customer = low end drive where you will not pay twice the
price for 10% performance increase.

There is nothing there about reliability !!!
Now every [sane] storage engineer will chose a "customer" 5.4k drives
for a cold storage / slow IO storage. In high demand, very random seek
patterns everybody will go for extreme fast disk that will die in 12
months, because cost * effort or replacing a failed disk is still less
than assembling a like array from 7.2k disk (extra controller, extra
bays, extra power, extra everything !).

So:
1.
Stop reading a marketing material that is designed to suck money out
of you pocket. Read technical datasheet.
Stop reading a paid for articles from so called "specialists", my
company pays those people to put in articles that I write to sound
more technical so I can tell you how much "horse" those are.

2.
hdd:
faster rpm = better seek + better sequential read write
slower rpm = survives longer + takes less power + better $ per GB

3.
what you need to use it for:
a remote nas box ? a single 5.1k hdd will saturate your gigabit lan, 7
will saturate your SFP+ - go for best $ per GB
local storage ? 4 x 7.1k hdd in raid10 and you're talking a good
performance ! putting more disks in and you can drop down to 5.1k
a high demand database with thousands of people punching milions of
queries a second ? 15k as many as you can!

4.
For time being on btrfs give raid 5 & 6 a wide berth for time being
... unless you back up your data [very] regularly than, have fun :)

Re: raid levels and NAS drives

[Peter Becker]

>From experience, for a video-archiv and backup-server its not a
problem to use desktop drives if you respect the following thinks:

1. Avoid stock "green"-drives; For example, use the WD Idle tool to
stop excessive load cycles for WD Green drives
2. Desktop drives didn't have time-limited error recovery (TLER); if
you have bad sectores. the drive will try to read the sectore for 1-2
minutes
3. Avoid the cheap toshiba 5TB drives .. :)

I have i use: 3x WD Green 3TB, 1x WD Red 3TB, 1x WD Red 6TB, 1x Seagate NAS 3TB

Re: raid levels and NAS drives

[Austin S. Hemmelgarn]

On 2016-10-09 19:12, Charles Zeitler wrote:
> Is there any advantage to using NAS drives
> under RAID levels,  as oppposed to regular
> 'desktop' drives for BTRFS?
Before I answer the question, it is worth explaining the differences 
between the marketing terms 'desktop', 'enterprise', 'NAS', and 'video' 
as they relate to hard drives.

The big distinguishing factors that make a hard drive a 'desktop' drive 
are that it will retry reading a bad sector for an insanely long time 
(multiple minutes on most drives), it usually won't run at more than 
7200 RPM, and it may have better energy efficiency and be designed to 
handle more load/unload cycles for the heads (that is, it's designed for 
regular desktop/laptop usage patterns).

An 'enterprise' drive by contrast has support for setting the read 
timeout and write timeout on bad sectors (variously called TLER, SCT 
ERC, and numerous other things), typically runs at higher speeds (10k or 
15k RPM), and is usually designed for continuous 24/7 operation.

A 'NAS' drive is somewhere between a 'desktop' and an 'enterprise' 
drive, they have TLER/ERC, but usually don't run at more than 7200 RPM, 
and are usually designed with energy efficiency in mind.

A 'video' or 'security' drive is a special case that's only marketed by 
WD as far as I know, they're designed for low error rate, 24/7 
operation, and very high performance streaming writes and reads.

So, as for what you should use in a RAID array, here's my specific advice:
1. Don't worry about enterprise drives unless you've already got a 
system that has them.  They're insanely overpriced for relatively 
minimal benefit when compared to NAS drives.
2. If you can afford NAS drives, use them, they'll get you the best 
combination of energy efficiency, performance, and error recovery.
3. If you can't get NAS drives, most desktop drives work fine, but you 
will want to bump up the scsi_command_timer attribute in the kernel for 
them (200 seconds is reasonable, just make sure you have good cables and 
a good storage controller).
4. Avoid WD Green drives, without special effort, they will get worse 
performance and have shorter lifetimes than any other hard disk I've 
ever seen.
5. Generally avoid drives with a capacity over 1TB from manufacturers 
other than WD, HGST, and Seagate, most of them are not particularly good 
quality (especially if it's an odd non-power-of-two size like 5TB).

Re: raid levels and NAS drives

[Nicholas D Steeves]

On Mon, Oct 10, 2016 at 08:07:53AM -0400, Austin S. Hemmelgarn wrote:
> On 2016-10-09 19:12, Charles Zeitler wrote:
> >Is there any advantage to using NAS drives
> >under RAID levels,  as oppposed to regular
> >'desktop' drives for BTRFS?
[...]
> So, as for what you should use in a RAID array, here's my specific advice:
> 1. Don't worry about enterprise drives unless you've already got a system
> that has them.  They're insanely overpriced for relatively minimal benefit
> when compared to NAS drives.
> 2. If you can afford NAS drives, use them, they'll get you the best
> combination of energy efficiency, performance, and error recovery.
> 3. If you can't get NAS drives, most desktop drives work fine, but you will
> want to bump up the scsi_command_timer attribute in the kernel for them (200
> seconds is reasonable, just make sure you have good cables and a good
> storage controller).
> 4. Avoid WD Green drives, without special effort, they will get worse
> performance and have shorter lifetimes than any other hard disk I've ever
> seen.
> 5. Generally avoid drives with a capacity over 1TB from manufacturers other
> than WD, HGST, and Seagate, most of them are not particularly good quality
> (especially if it's an odd non-power-of-two size like 5TB).

+1 !  Additionally, is it still the case that it is generally safer to
buy the largest capacity disks offered by the previous generation of
technology rather than the current largest capacity?  eg: right now
that would be 4TB or 6TB, and not 8TB or 10TB.

Cheers,
Nicholas

Re: raid levels and NAS drives

[Austin S. Hemmelgarn]

On 2016-10-11 18:10, Nicholas D Steeves wrote:
> On Mon, Oct 10, 2016 at 08:07:53AM -0400, Austin S. Hemmelgarn wrote:
>> On 2016-10-09 19:12, Charles Zeitler wrote:
>>> Is there any advantage to using NAS drives
>>> under RAID levels,  as oppposed to regular
>>> 'desktop' drives for BTRFS?
> [...]
>> So, as for what you should use in a RAID array, here's my specific advice:
>> 1. Don't worry about enterprise drives unless you've already got a system
>> that has them.  They're insanely overpriced for relatively minimal benefit
>> when compared to NAS drives.
>> 2. If you can afford NAS drives, use them, they'll get you the best
>> combination of energy efficiency, performance, and error recovery.
>> 3. If you can't get NAS drives, most desktop drives work fine, but you will
>> want to bump up the scsi_command_timer attribute in the kernel for them (200
>> seconds is reasonable, just make sure you have good cables and a good
>> storage controller).
>> 4. Avoid WD Green drives, without special effort, they will get worse
>> performance and have shorter lifetimes than any other hard disk I've ever
>> seen.
>> 5. Generally avoid drives with a capacity over 1TB from manufacturers other
>> than WD, HGST, and Seagate, most of them are not particularly good quality
>> (especially if it's an odd non-power-of-two size like 5TB).
>
> +1 !  Additionally, is it still the case that it is generally safer to
> buy the largest capacity disks offered by the previous generation of
> technology rather than the current largest capacity?  eg: right now
> that would be 4TB or 6TB, and not 8TB or 10TB.
In general, yes, but you're normally safe as long as you're not using 
SMR disks.  I've used a couple of 8TB non-SMR drives, and they work 
perfectly fine (although they're insanely expensive), it's just been the 
SMR stuff that's been an issue (and you shouldn't be using them for 
non-archival storage anyway).