SMR or SSD disks?

SMR or SSD disks?

[Gandalf Corvotempesta]

Hi guys
i'm doing some maintenance replacing some not-yet-failed HDD with WD RED SSD.
I've read the warning on the homepage
https://raid.wiki.kernel.org/index.php/Linux_Raid

Are SSD drives still subject to SMR ? I've thought that it was related
only to magnetic drives not on SSD.

in example i have a WDC  WDS200T1R0A (WD RED SA500), is this subject
to SMR and I have to replace it anyway ? (i've added it to the raid
right now, moving from a 2 way mirror to a 3 way mirror)

If I have to replace them, which 2TB SSD should I use ? Usually i've
used Samsung SSD but i've read some bad reviews on newer models.

Any suggestions ? Ideas ?

Re: SMR or SSD disks?

[Andy Smith]

Hello,

On Sun, Nov 26, 2023 at 11:18:39AM +0100, Gandalf Corvotempesta wrote:
> i'm doing some maintenance replacing some not-yet-failed HDD with WD RED SSD.
> I've read the warning on the homepage
> https://raid.wiki.kernel.org/index.php/Linux_Raid
> 
> Are SSD drives still subject to SMR ? I've thought that it was related
> only to magnetic drives not on SSD.

SMR is not applicable to flash-based storage. I expect the warning
on the wiki was written at a time when the only drives bearing the
WD Red brand were HDDs, not any SSDs.

Thanks,
Andy

Re: SMR or SSD disks?

[Hannes Reinecke]

On 11/26/23 11:37, Andy Smith wrote:
> Hello,
> 
> On Sun, Nov 26, 2023 at 11:18:39AM +0100, Gandalf Corvotempesta wrote:
>> i'm doing some maintenance replacing some not-yet-failed HDD with WD RED SSD.
>> I've read the warning on the homepage
>> https://raid.wiki.kernel.org/index.php/Linux_Raid
>>
>> Are SSD drives still subject to SMR ? I've thought that it was related
>> only to magnetic drives not on SSD.
> 
> SMR is not applicable to flash-based storage. I expect the warning
> on the wiki was written at a time when the only drives bearing the
> WD Red brand were HDDs, not any SSDs.
> 
Correct. Typically SATA SSDs do not expose SMR capabilities; it's all
hidden by the FTL there.

And the warning really is outdated. What matters is that the HDD needs
to support TLER (ie scterc capabilities); the brand or series really is 
immaterial. There are plenty of non-SMR HDDs which do not support it. 
Sadly it's not well advertised, so you really have to test
(or invest in the HDD range which is geared up for this kind of usage.)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Ivo Totev, Andrew McDonald,
Werner Knoblich

Re: SMR or SSD disks?

[Wols Lists]

On 26/11/2023 11:55, Hannes Reinecke wrote:
> On 11/26/23 11:37, Andy Smith wrote:
>> Hello,
>>
>> On Sun, Nov 26, 2023 at 11:18:39AM +0100, Gandalf Corvotempesta wrote:
>>> i'm doing some maintenance replacing some not-yet-failed HDD with WD 
>>> RED SSD.
>>> I've read the warning on the homepage
>>> https://raid.wiki.kernel.org/index.php/Linux_Raid
>>>
>>> Are SSD drives still subject to SMR ? I've thought that it was related
>>> only to magnetic drives not on SSD.
>>
>> SMR is not applicable to flash-based storage. I expect the warning
>> on the wiki was written at a time when the only drives bearing the
>> WD Red brand were HDDs, not any SSDs.

Yes. The WD Red line was always advertised as "optimised for raid" 
(which was debatable, but okay), then they switched it to SMR. So the 
notice was saying "keep away !!!". I think several new SMR Reds failed 
badly when people tried to rebuild their array.
>>
> Correct. Typically SATA SSDs do not expose SMR capabilities; it's all
> hidden by the FTL there.

If you look at what SMR is, it's only relevant to spinning rust. It 
relies on the fact that a read head can be much smaller than a write 
head, so provided you shingle your writes (hence the name), you can 
over-write half the previous track (so saving space) without rendering 
the data unreadable.

The problem is you have to stream your writes, you can't go back, which 
is why these drives - especially the early ones - had a habit of 
stalling for minutes on end, as they shuffled stuff around.
> 
> And the warning really is outdated. What matters is that the HDD needs
> to support TLER (ie scterc capabilities); the brand or series really is 
> immaterial. There are plenty of non-SMR HDDs which do not support it. 
> Sadly it's not well advertised, so you really have to test
> (or invest in the HDD range which is geared up for this kind of usage.)
> 
I'm not sure how true that is now, I've not been keeping up. But about 
that time (2020), most desktop drives - the sort that don't have TLER - 
were transitioning to SMR. Hence the warning following immediately - 
don't use desktop drives! I suspect non-SMR is now a premium feature 
which will usually come with TLER as a matter of course.

As I say, I'm not up-to-date any more. If anybody can give me some 
facts, I'll happily update the site.

Cheers,
Wol

Re: SMR or SSD disks?

[Peter Grandi]

>>> Are SSD drives still subject to SMR ? I've thought that it
>>> was related only to magnetic drives not on SSD.

Indeed SMR is a magnetic recording technique that potentially
results in very expensive read-modify-write operations.

> And the warning really is outdated. What matters is that the
> HDD needs to support TLER (ie scterc capabilities)

SCT/ERC/TLER is indeed an important feature in case HDD fail
*and* long latencies (like 30-100s) are not a good idea. Most
SSD either have SCT/ERC/TLER or don't need it as their retry
cycles are very short. What matters more is setting the Linux
driver retry timeout (which ought to be must always be higher
than that of the drive)

SSDs can have different issues that are undesirable for most
"business" applications, usually:

* Volatile write buffers (lack of "Power Loss Protection").

* Low endurance (low Device Writes Per Day).

* Potential high latencies in mixed workloads (interleaved read
  and write streams).

* Long term reduction in data transfer rates because
  FTL "compaction" cannot run faster than erase block
  fragmentation.

These can all affect an MD RAID set, in particular if bitmaps or
write logs are used or if the workload is challenging.

Re: SMR or SSD disks?

[Gandalf Corvotempesta]

Il giorno dom 26 nov 2023 alle ore 13:22 Wols Lists
<antlists@youngman.org.uk> ha scritto:
> If you look at what SMR is, it's only relevant to spinning rust. It
> relies on the fact that a read head can be much smaller than a write
> head, so provided you shingle your writes (hence the name), you can
> over-write half the previous track (so saving space) without rendering
> the data unreadable.

Thank you all.
That's what i've thought but better stay safe than sorry so i've asked.

In other words WD Red SSD are safe for a RAID, there is no need to change them
(as mostly new) in both array (the grow was finished 1 hour ago: 2 WD
Gold SATA 3.5 plus 1 WD RED SSD)

Slowly, i'll replace all spinning disks with WD Red SSD
I'm not a fan of WD, but 2TB disks able to replace a 2TB HDD are very
very rare (the 1.92TB, much more common, can't replace a 2TB disk)

Re: SMR or SSD disks?

[Roman Mamedov]

On Sun, 26 Nov 2023 23:22:51 +0100
Gandalf Corvotempesta <gandalf.corvotempesta@gmail.com> wrote:

> Il giorno dom 26 nov 2023 alle ore 13:22 Wols Lists
> <antlists@youngman.org.uk> ha scritto:
> > If you look at what SMR is, it's only relevant to spinning rust. It
> > relies on the fact that a read head can be much smaller than a write
> > head, so provided you shingle your writes (hence the name), you can
> > over-write half the previous track (so saving space) without rendering
> > the data unreadable.
> 
> Thank you all.
> That's what i've thought but better stay safe than sorry so i've asked.
> 
> In other words WD Red SSD are safe for a RAID, there is no need to change them
> (as mostly new) in both array (the grow was finished 1 hour ago: 2 WD
> Gold SATA 3.5 plus 1 WD RED SSD)
> 
> Slowly, i'll replace all spinning disks with WD Red SSD
> I'm not a fan of WD, but 2TB disks able to replace a 2TB HDD are very
> very rare (the 1.92TB, much more common, can't replace a 2TB disk)

There are three grades of capacity that you can get:
1) ~1920 000 000 000 bytes
2) ~2000 000 000 000 bytes
3) ~2048 000 000 000 bytes

Nobody is marketing the 1st variant as "2TB", you will find "1920G" on the
packaging and datasheets instead.

2nd one should be able to replace an HDD, unless there's some smaller
discrepancy in the sizes near the 2 billion byte mark between HDDs and SSDs. A
reason to use smaller-than-whole-disk partitions for your RAID.

3rd is not a common sight in SATA SSDs (but still happens), and is nearly
universal in NVMe. Of about ten "2 TB" NVMe models I've tested, only one had
2000, *all* others were 2048. The 2000 one was Netac NV7000.

-- 
With respect,
Roman

Re: SMR or SSD disks?

[Gandalf Corvotempesta]

yes i know, but the most common SSD size is 1.92 , at least here in my country.

and the raid i have to upgrade is made with 2tb spinning disks.

(i don't have support for nvme on these old servers)

Il giorno lun 27 nov 2023 alle ore 00:08 Gandalf Corvotempesta
<gandalf.corvotempesta@gmail.com> ha scritto:
>
> yes i know, but the most common SSD size is 1.92 , at least here in my country.
>
> and the raid i have to upgrade is made with 2tb spinning disks.
>
> (i don't have support for nvme on these old servers)
>
> Il dom 26 nov 2023, 23:52 Roman Mamedov <rm@romanrm.net> ha scritto:
>>
>> On Sun, 26 Nov 2023 23:22:51 +0100
>> Gandalf Corvotempesta <gandalf.corvotempesta@gmail.com> wrote:
>>
>> > Il giorno dom 26 nov 2023 alle ore 13:22 Wols Lists
>> > <antlists@youngman.org.uk> ha scritto:
>> > > If you look at what SMR is, it's only relevant to spinning rust. It
>> > > relies on the fact that a read head can be much smaller than a write
>> > > head, so provided you shingle your writes (hence the name), you can
>> > > over-write half the previous track (so saving space) without rendering
>> > > the data unreadable.
>> >
>> > Thank you all.
>> > That's what i've thought but better stay safe than sorry so i've asked.
>> >
>> > In other words WD Red SSD are safe for a RAID, there is no need to change them
>> > (as mostly new) in both array (the grow was finished 1 hour ago: 2 WD
>> > Gold SATA 3.5 plus 1 WD RED SSD)
>> >
>> > Slowly, i'll replace all spinning disks with WD Red SSD
>> > I'm not a fan of WD, but 2TB disks able to replace a 2TB HDD are very
>> > very rare (the 1.92TB, much more common, can't replace a 2TB disk)
>>
>> There are three grades of capacity that you can get:
>> 1) ~1920 000 000 000 bytes
>> 2) ~2000 000 000 000 bytes
>> 3) ~2048 000 000 000 bytes
>>
>> Nobody is marketing the 1st variant as "2TB", you will find "1920G" on the
>> packaging and datasheets instead.
>>
>> 2nd one should be able to replace an HDD, unless there's some smaller
>> discrepancy in the sizes near the 2 billion byte mark between HDDs and SSDs. A
>> reason to use smaller-than-whole-disk partitions for your RAID.
>>
>> 3rd is not a common sight in SATA SSDs (but still happens), and is nearly
>> universal in NVMe. Of about ten "2 TB" NVMe models I've tested, only one had
>> 2000, *all* others were 2048. The 2000 one was Netac NV7000.
>>
>> --
>> With respect,
>> Roman

Re: SMR or SSD disks?

[Reindl Harald]

Am 27.11.23 um 09:11 schrieb Gandalf Corvotempesta:
> yes i know, but the most common SSD size is 1.92 , at least here in my country.
> and the raid i have to upgrade is made with 2tb spinning disks.

i started to replace HDDs with "Samsung Evo 850 2 TB" 7 years ago
in which country you coudn't buy them (now 870) from Amazon 2023?

Re: SMR or SSD disks?

[Gandalf Corvotempesta]

Il giorno lun 27 nov 2023 alle ore 10:15 Reindl Harald
<h.reindl@thelounge.net> ha scritto:
> i started to replace HDDs with "Samsung Evo 850 2 TB" 7 years ago
> in which country you coudn't buy them (now 870) from Amazon 2023?

Samsung are my first choise for desktop drives, (second choice, after
intel, for the DC drives)
but i've read somewhere that the latest SSDs had some issues,
particularly under linux, with a
lot of write errors, that's why i've purchased a different brand (and,
honestly, I hate WD)

Did you had any issue with the Evo drives under RAID ?

Re: SMR or SSD disks?

[Gandalf Corvotempesta]

Il giorno lun 27 nov 2023 alle ore 13:35 Gandalf Corvotempesta
<gandalf.corvotempesta@gmail.com> ha scritto:
> but i've read somewhere that the latest SSDs had some issues,
> particularly under linux, with a
> lot of write errors, that's why i've purchased a different brand (and,
> honestly, I hate WD)

In example
https://www.techpowerup.com/forums/threads/samsung-870-evo-beware-certain-batches-prone-to-failure.291504/

Re: SMR or SSD disks?

[Reindl Harald]

Am 27.11.23 um 13:35 schrieb Gandalf Corvotempesta:
> Il giorno lun 27 nov 2023 alle ore 10:15 Reindl Harald
> <h.reindl@thelounge.net> ha scritto:
>> i started to replace HDDs with "Samsung Evo 850 2 TB" 7 years ago
>> in which country you coudn't buy them (now 870) from Amazon 2023?
> 
> Samsung are my first choise for desktop drives, (second choice, after
> intel, for the DC drives)
> but i've read somewhere that the latest SSDs had some issues,
> particularly under linux, with a
> lot of write errors, that's why i've purchased a different brand (and,
> honestly, I hate WD)
> 
> Did you had any issue with the Evo drives under RAID ?

no

i have 2/4 TB 850/860/870 over the past years in several machines with 
RAID1 and RAID10 without any issue

Re: SMR or SSD disks?

[Reindl Harald]

Am 27.11.23 um 13:36 schrieb Gandalf Corvotempesta:
> Il giorno lun 27 nov 2023 alle ore 13:35 Gandalf Corvotempesta
> <gandalf.corvotempesta@gmail.com> ha scritto:
>> but i've read somewhere that the latest SSDs had some issues,
>> particularly under linux, with a
>> lot of write errors, that's why i've purchased a different brand (and,
>> honestly, I hate WD)
> 
> In example
> https://www.techpowerup.com/forums/threads/samsung-870-evo-beware-certain-batches-prone-to-failure.291504/

my 870 are from 2022 and most likely not affacted at all
these seem to be early produced ones

when you make decisions on such threads you can't buy anything at all no 
matter SSD or HDD - Samsgung SSD at least have some reputation over the 
past 10 years

Re: SMR or SSD disks?

[Gandalf Corvotempesta]

Il giorno lun 27 nov 2023 alle ore 18:23 Reindl Harald
<h.reindl@thelounge.net> ha scritto:
> my 870 are from 2022 and most likely not affacted at all
> these seem to be early produced ones
>
> when you make decisions on such threads you can't buy anything at all no
> matter SSD or HDD - Samsgung SSD at least have some reputation over the
> past 10 years
>

thank you so much
i'll order a couple of them...