Seagate Exos 2x14: Die perfekte 14TB HDD für die Unraid Parität?


mgutt

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Update:

Leider doch nicht, da sich die Festplatte als 2 Festplatten mit jeweils 7TB ausgibt:

https://forums.unraid.net/topic/103248-seagate-mach2-in-unraid/?tab=comments#comment-952853

 

Ursprünglicher Beitrag:

Die erste HDD mit zwei unabhängigen Lese- / Schreibköpfen. Spezifiziert auf 500 MB/s:

https://www.seagate.com/files/www-content/datasheets/pdfs/exos-2x14-DS2015-2-1912DE-de_DE.pdf

1213754986_2021-03-2217_19_28.png.311837bf83b44ada0e5b67548a1e50fb.png

 

Paralleles Lesen und Schreiben wie bei der Unraid Parität, könnten davon massiv profitieren. Wenn sich dadurch die Schreibgeschwindigkeit der normalen Exos verdoppelt, sollten damit in Zukunft im Unraid Array 160 MB/s möglich sein. Also Turbo-Write ohne Turbo-Write aktivieren zu müssen ;)

 

Jetzt fehlt nur noch der Preis, aber für die doppelte Performance, darf die denke ich ruhig was mehr kosten. Man braucht sie ja auch nur in der Parität.

 

Bisher leider nur als SAS angekündigt. Ich hoffe davon kommt auch eine SATA Version.

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Wenn die Serie Erfolg hat, bringt Seagate vielleicht ja auch ein Modell raus, wo sie sich als eine HDD ausgibt. Wobei die Sektoren bei der Zählung dann aber ständig zwischen unterer und oberer Ebene wechseln müssen. Sonst hätte man keinen "Stripping-Effekt", der ja erst die Geschwindigkeit erhöht. Also eine Art RAID0 auf Hardwareebene.

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  • 1 year later...
4 hours ago, frodr said:

I found this, and placed a PO for the SATA version. Die frage: Supportiert unRaid die Mach.2 Technologie?

[antwort in englich, weil ich nicht weiss, ob es in deutsch verstanden würde. Sollte jemand es in deutsch wünschen, kann ich es gerne nochmal in deutsch formulieren.]

[answer in english. because i don't know if you can understand it in german.]

 

I guess there is nothing to support, since the interface has to follow the specified standard.

 

I read that PDF and guess (without actual experiencing that type of disk):

There Seagate mentions the disks with different Interfaces (and correcponding different data in the tables).

But all the the disks have only  half the capacity  per actuator.

 

I don't know how Seagate uses that fact in the SATA Disks, but the SAS are mentioned with also half the capacity per logical unit (and SAS can adress multi devices/disks over one physical connection).

(Without practical experience from my side) I guess Seagate handle 'double actuator' like WD:

WD just released their first "Double Actuator" Disk (only SAS interface) and there it seems a disc-case with 20TB will be handled like 2 seperate disks (=logical units) with each 10 TB.

That way you may save physical space in only installing 1 diskcase, but in reality you dont get (almost) any speed/performance benefit per logical unit.

It just handles like 2 seperate disks inside of one discase.

And since it will be handled like two disks, both are almost the same speed like an original 10TB Disk because physicas do not change for the read-/write heads over the exclusively used platter in the disc-case. Each Head only has its exclusive platter and the other head only uses an other platter.

(head means here the comb with multiple heads).

Here a german article about the WD release

https://www.heise.de/news/Western-Digital-Doppel-Aktuator-verdoppelt-Festplatten-Performance-7477075.html

 

Now back to Seagate and SATA:

But since SATA does normally (without multilane) not support 2 devices at one physical connection, Seagate must have made somthing different between their SAS and SATA Disks firmware. So you may be the first to tell us if this technology really has an advantade and the firmware will virtually act as if the sata disk is really only one big logical unit.

 

But even when it acts as one big logical unit, the dual actuators work on different platters.

So there will be (almost) no speed benefit in using as parity.

That is because parity is build by

1. reading one sector,

2. calculating the new value,

3. waiting until the same sector is again under the same read-/wrtite-head and

4. writing the same sector.

That whole process can't be split up to 2 different platter, because when you split it to two actuators, it will not be the same sector read and written.

 

So I guess that concept may be really nice if you read oder write a whole bunch of data to the single diskcase (Server-Enterprice enviroments and just add the 2 different datastreams with a big cache in between) and use multi streams. But if you use sequential read or write (like in Array opertaions in unraid it can't surpass the physical limitation of the one actuator that has the needed sector unter 'its thumb'.

And even if this technology is a litte bit more modern/advanced and so may be a litte bit faster, it will not be the double performance in singlestream operations.

 

Sorry for my bad english.

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8 hours ago, frodr said:

I found this, and placed a PO for the SATA version. Die frage: Supportiert unRaid die Mach.2 Technologie?

 

Interesting find. Now the datasheet says "or one 18TB logical device for SATA". As SATA is SATA, I would say yes. But it has a huge power consumption 😔 

 

Note: If you consider this drive as a parity drive, then your other 18TB drives must be exactly equal or smaller in size. And yes, not every 18TB drive has the same size!

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4 hours ago, Dtrain said:

only write or read at double speed

The article is talking about the "serial" in SATA which is in theory correct, but reads and writes are split into chunks and processed in a queue, so it finally allows "parallel" reading and writing. But of course much slower than having multiple lanes.

 

I would expect around 150 - 200 MB/s with a dual actuator parity disk while writing to the array.

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