SSD Cache

[LordGrande]

Hi All!

Im new on this forum, i was using TrueNas a couple of years because i was looking for a NAS System with good scalability and performance and in other hand i was looking for a low power server.
So the specs of my server are the following:

• Motherboard: Asrock rack c3758d4i-4l
• Ram: 16Gb x 4 ECC 2133mhz DDR4
• PSU: Unykach 250w 80 plus platinum
• Storage: 4x HDD of 4TB in raidz2 with 1 SSD Sata of 120GB for LOG and 1 SSD Sata of 120GB for Cache
• Boot: 2x SSD 64GB Mirror

Its a home server, im use this server for storage my persona data, my work data using ISCSI and some ISOs and VM Disk for my Proxmox server (but the Proxmox server its normally off, its just for entertainment).
Im also running some plugins like NextCloud, Plex and MineOs... and im looking for a DNS plugins too for replace my PiHole server.

I have the following doubts:
Im not very sure how the ssd cache/log works, i was reading some thread and maybe in my case its not recommended, because for read 4x HDD vs 1 Sata SSD i think doesnt make any different and for write (its the ssd for LOG, right?) its the same.
But, maybe the cache/log helps not to use the hdd very often which translates into lower power consumption... im right? or not?
Otherwise, im thinking that maybe i can use thats 2 SSD for my plugins, not for better performance, just for not use the hdd very often.

So in resume, im need your help for decided, its better for me kept one sata SSD for cache and other for LOG or use them for my plugins?
What are the pros and cons? Im going to lose performance removing the SSDs?

Thank you all for all yours response,
If anyone can share a link with a great course or somethink like that about TrueNas, i would thank that very much.

 

[NugentS]

a SLOG only works with sync writes. NFS and iSCSI
As long as you have set sync=enabled (or standard I think) then the SLOG will be doing something
The "Cache" - I don't know what that is - but its probably L2ARC, in which case it might be doing something, or might not depending on workload.

I don't think either will help with power use.

 

[LordGrande]

Thank you very much NugentS, but your comment no solved my doubts,
So, yes, probably the LOG/L2ARC ssds are doing something and maybe the ssds are not helping with the power user....

Im going to explain another time my doubts, maybe i was not clear, its my first time trying to explain this and in other languages... and i still confused with this topic.
Knowing that I can only add up to 3 sata ssds:

• How can increase my reading speed?
• How can increase my writing speed?
• Using SSDs for cache, i can save power?
• Maybe its more usefull use the ssds just for the plugins?

I was investigating that if I had only one ssd for LOG and it got damaged it could corrupt my data, so I decided to put both ssds (the one for LOG and the one for Cache) in mirror while im investing...

Thank you!
PD: Sorry if i sound rude, its not my purpose, i only want to learn well.

 

[jgreco]

• How can increase my reading speed?
• How can increase my writing speed?

Difficult, probably cannot, at least not much.

Using SSDs for cache, i can save power?

Cannot/false/no.

Maybe its more usefull use the ssds just for the plugins?

Possibly/yes.

I had only one ssd for LOG and it got damaged it could corrupt my data

Mostly false.

the one for LOG and the one for Cache) in mirror while im investing...

Probably not helpful and not useful.

Sorry if i sound rude, its not my purpose, i only want to learn well.

No worries. You are not offending anyone. We are happy to try to help.

My comments, distilled into short bits that I hope translate well:

RAIDZ2 is not good for iSCSI, though the amount of "hurt" you get from this may not be that large.

The path to success for block storage

It seems like I haven't written a sticky for awhile, but just in the last week I've had to cover this topic several times. ZFS does two different things very well. One is storage of large sequentially-written files, such as archives, logs, or data files, where the file does not have the middle...

www.truenas.com

RAIDZ2 is pretty good for large file storage, and normally it gives you performance that is as good as you're going to get easily. So you may be best off with RAIDZ2.

L2ARC only helps with stuff you read a lot.

SLOG is not very helpful for home users with small systems. SLOG is always slower than async writes.

I think it would be difficult to improve your system with L2ARC or SLOG.

 

[Etorix]

So the specs of my server are the following:

• Motherboard: Asrock rack c3758d4i-4l
• Ram: 16Gb x 4 ECC 2133mhz DDR4
• PSU: Unykach 250w 80 plus platinum
• Storage: 4x HDD of 4TB in raidz2 with 1 SSD Sata of 120GB for LOG and 1 SSD Sata of 120GB for Cache
• Boot: 2x SSD 64GB Mirror

Congratulations on the build. Nice small server board (experts may want to weight in on the Marvell 88E1543 NIC…), L2ARC that is not oversized (rather the opposite) for 64 GB RAM, that's not too far from the textbook.
250 W PSU is too small for adding more disks in the future.

Knowing that I can only add up to 3 sata ssds:

• How can increase my reading speed?
• How can increase my writing speed?

Wider raidz vdevs, more vdevs. So you're somewhat stuck.

What's the size of the working dataset for your 2-3 users? If it fits in whatever RAM is left by the system and VMs (30-40 GB), L2ARC is not useful. If the working dataset is larger than 120 GB, then the current L2ARC is too small.

Disabling sync writes could speed up write… at risk for the iSCI share.
With sync writes, a SLOG may help, but note that the SLOG is only secure if it has Power-Loss-Protection (e.g. Intel DC S3700); a consumer SSD does no good in this function.

Some insights into SLOG/ZIL with ZFS on FreeNAS

What is the ZIL? POSIX provides a facility for the system or an application to make sure that data requested to be written is actually committed to stable storage: a synchronous write request. Upon completion of a sync write request, the underlying filesystem is supposed to guarantee that a...

www.truenas.com

 

[NugentS]

Thank you very much NugentS, but your comment no solved my doubts,
So, yes, probably the LOG/L2ARC ssds are doing something and maybe the ssds are not helping with the power user....

Im going to explain another time my doubts, maybe i was not clear, its my first time trying to explain this and in other languages... and i still confused with this topic.
Knowing that I can only add up to 3 sata ssds:

• How can increase my reading speed?
• How can increase my writing speed?
• Using SSDs for cache, i can save power?
• Maybe its more usefull use the ssds just for the plugins?

I was investigating that if I had only one ssd for LOG and it got damaged it could corrupt my data, so I decided to put both ssds (the one for LOG and the one for Cache) in mirror while im investing...

Thank you!
PD: Sorry if i sound rude, its not my purpose, i only want to learn well.

Basically what @jgreco and@Etorix say - but I shall expand a bit and ignore your physical limitations on hard disks and PSU limit

• How can increase my reading speed?
  • By adding more disks in more vdevs
• How can increase my writing speed?
  • By adding more disks in more vdevs
• Using SSDs for cache, i can save power?
  • No
• Maybe its more usefull use the ssds just for the plugins?
  • Probably

One SSD for SLOG - corrupting data. Its possible BUT the disk would have to fail AND the server would have to crash for this to be potentially an issue. Obviously mirrored is better but the corrupted data is fairly edge case. Note that the SLOG disk(s) needs to have Power Loss Protection to be fully effective and actually perform its most important task as @Etorix says.

Read the articles that both the aforementioned experts have pointed out which will answer your questions in far more detail than I care to type

 

[LordGrande]

Thank you very much to all of you!!

So.. well, i was reading everything and in resume:
- Sata SSDs for SLOG/L2ARC... its not going to give me anything
- Sata SSDs for my plugins yes, so im think that im going to create a new mirror pool with the sata ssds and im going to move all the plugins to that pool.
- Save power.. Nop

And in other hand, there was 2 topics that make me think:
- RaidZ2: I upgrade my server recently, i brought a new case with space for 8 hot swap hdd and i brought 2 more hdds (for the total of 4)... So, my old pool was mirror and i move all the data to my new pool in RaidZ2 indeed of upgrade my existing mirror pool.... because i was planing in buy more hdds in a future thinking that RaidZ2 for 8 hdd its better than a mirror pool of 8 hdd.. and no, for me its better keep mirroring hdd for better performance. I will keep the RaidZ2 until the next upgrade, because... well... for me its a scary job, but i will keep that in mind.
- PSU: It's clear that you are the experts here but I don't entirely agree with you. I recently buy a "killer a watt" (that thing for mesuare the power) and the readings when i use it are 70w running all the plugins and tranfering data, at start 50w and in IDLE 40w and i was very surprise because that its a very little energy... Doing calculations, i think, maybe, the motherboard+cpu+ram spent 50 w and each HDD 10w at full (the exact model for my hdd are Seagate ST4000VN008).. So if i add 4 more disks to my configuration, i think i will not have any problem.
Anyway, if anybody knows a cheap 80 plus platinum PSU for 2U, please share the link, i will appreciate it, because im going to need one in a future for others builds.


Again, thank you all very much!!

 

[NugentS]

Its not nessesarily the total power whilst running. Its the power on specific lines during startup that can be an issue, like the 5V

 

[jgreco]

I don't entirely agree with you.

You don't have to agree. However, please note that I do this stuff professionally with an engineering background. I explain the how and why of calculating this properly in the following article:

Proper Power Supply Sizing Guidance

I've seen about 1,000 threads like this one where people decide that they can power a dozen hard drives off a 360 watt supply. DO NOT DO THIS. I've seen another 1,000 threads where people decide to buy the cheapest power supply that they can find. DO NOT DO THIS. Your NAS lives or dies by...

www.truenas.com

I respect anyone's right to make their own mistakes, but I'd really like for people to make those mistakes being well-informed. A NAS contains too many expensive parts to get hosed over by a incorrectly sized PSU.

 

[Ericloewe]

I recently buy a "killer a watt" (that thing for mesuare the power) and the readings when i use it are 70w running all the plugins and tranfering data, at start 50w and in IDLE 40w and i was very surprise because that its a very little energy...

Important note: Measurements of fast transients, like the server turning on, are not really the domain of cheap consumer power meters.

 

[HoneyBadger]

"Inrush current" is the phrase you should search for and do some research on @LordGrande

How to Measure Inrush Current

Knowing the value of inrush current helps technicians locate startup problems

www.fluke.com

Inrush current can be 4 to 10 times greater than the normal running current, depending on the type of motor.

You will not be able to measure this with a passthrough "power meter" like a Kill-A-Watt.

 

[jgreco]

"Inrush current" is the phrase you should search for

Yup. All our storage servers leave the shop here with an inrush rating, and it has happened that I've had to tell a client that their rack isn't sufficiently provisioned to support a cold start. Sometimes even WITH staggered spinup setups, etc. Data center power is expen$$$$ive so people try to cheat.

 

[LordGrande]

Sorry for the delay,

Thank you all!! After read everything im more informed about what power supply should i have... its was very interesting read thats threads

I was looking for these options:

- Seasonic SS-500-L2U-500W-2U:

Seasonic SS-500 L2U 500W 2U Gris unidad de fuente de alimentación, Fuente de alimentación de PC plateado, 500 W, 100 - 240, 50 - 60, Activo, 100 W, 480 W, A granel

Voltaje de entrada AC: 100 - 240, Frecuencia de entrada AC: 50 - 60. Diámetro de ventilador: 6 cm. Tipo de cableado: Modular. Utilizar con: PC, Fac...

www.alternate.es

- Inter-Tech Aspower-R2A-DV0550-N

Inter-Tech Aspower R2A-DV0550-N unidad de fuente de alimentación 550 W 20+4 pin ATX Acero inoxidable, Fuente de alimentación de PC gris, 550 W, 115 - 230 V, 92%, Sobreintensidad, Sobretensión, Sobrevoltaje, Sobrecalentamiento, Cortocircuito, 20+4 pin

Voltaje de entrada AC: 115 - 230 V, Eficiencia: 92%. Alimentador de energía para tarjeta madre: 20+4 pin ATX. Utilizar con: Servidor, Certificación...

www.alternate.es

I have the limitation of 2u size, i think that the Seasonic its enough for my NAS and its not very expensive
And the other one, the Inter-tech... well, is just a expensive whim, but maybe in the future i want to upgrade to other motherboard more powerfull and maybe create VMs directly on TrueNas Scale and not in proxmox...
And i dont care about spend money in the power supply, because the life of a power supply its too long BUT i dont want to spent more than the 300€ haha that number is too high for me

Any recomendation?