Concerns about RAM and ZFS Raid-Z

[Pnuts]

I purchased a HP ProLiant G7 N54L MicroServer and am finalizing my decision on what OS to use on it for a multi-purpose NAS. I really like but I am concerned about performance. I plan to use RAID-Z.

1. Reading through the documentation, it is recommended to use 1gb of ram per 1TB for ZFS. I plan to put four 2tb drives in the system and the system can support a maximum of 8gb of RAM.
2. If I am using plugins (Torrents, maybe plex), do you know how this will effect performance? Would it be horrible?
3. On that same note, I only will have 4gb of ram available when I set this up initially, will that create horrible performance until I can get the RAM upgraded to 8?
4. If I added eSata ports (assuming adding a PCIe card is supported) later and added additional drives, would I be able to add to the raid array or would I have to rebuild it/create a second array?
   • If I did this, it would put me well over 8tb against my 8gb RAM limit, would performance be horrible due to the RAM limitation?

Or based on the above, would you not recommend FreeNAS due to my limitations?

 

[warri]

Define horrible performance.

1. This will work, but you won't have any room for upgrades later.
2. See "define horrible performance"
3. I believe the system will be notably slower. But depending in your definition, it might be still fast enough for your use case.
4. Yes, but eSata is not necessarily recommended. Better get a bigger case to house more internal HDDs. You will have to add another vdev to the pool. See cyberjocks excellent beginners guide in the Noob section for details on ZFS.

 

[Pnuts]

Well, my current NAS (2x750gb Raid 1) is about 8 years old and averages about 20mb/s write and 40mb/s read on a gigabit network. I am hoping I will get much better then that, but I would say worse then that is horrible in my case.

After reading around more, I think I will use this as is and not plan for upgrades, instead replacing it once I start to out grow it like I am doing with my last NAS. From reading around, I think I will be okay with 8gb of RAM and 4x 2tb drives.

Thank you for your answers!

 

[warri]

Yeah, you should get a better performance. My rather low-end system can do roughly 40-50mb/s write and 70mb/s read.
Also the network card can cause serious performance drops, an Intel card/controller seems to work best.

 

[survive]

Hi Pnuts,

Keep in mind only mad men & thrill seekers use raidz1 with 4TB drives.

That Microserver will actually do 8GB DIMMs, look around and you can find a part number for the Kingston kit that has been proven to work.

-Will

 

[John M. Długosz]

I purchased a HP ProLiant G7 N54L MicroServer and am finalizing my decision on what OS to use on it for a multi-purpose NAS.

The summary I've seen is that this one (FreeNAS, up-to-date version) is designed with cheap RAM in mind so requires lots of it. OTOH, NAS4Free, the older code base, was made when hardware was less capable for the price, and is effectively deployed on old hand-me-down systems (that are less powerful than the new desktop machine).

But, HDD sizes have also gone up a great deal, and RAM scales with that to some extent. But for light use, does the server really need to keep details in RAM about everything on the drives? For archived material and a smaller current working set of files, I should think that the scaling is sub-linear.

 

[underpickled]

Keep in mind only mad men & thrill seekers use raidz1 with 4TB drives.

I agree, but I don't think anyone's talking about using 4TB drives in RAIDZ1

After reading around more, I think I will use this as is and not plan for upgrades, instead replacing it once I start to out grow it like I am doing with my last NAS. From reading around, I think I will be okay with 8gb of RAM and 4x 2tb drives.

 

[John M. Długosz]

<raising hand> I'm planning exactly that. I figured it was more efficient to use additional drives for off-line backups than for more stripes. The chance of a read-error during rebuilding is related to the amount of data stored, not the entire HDD size. So if I'm only storing 1.5TB of data for now, it doesn't matter that my drives could hold more. The comments on the infamous post push back on the extreme conclusion. Also, newer drives have better failure rates. (Anyone know the exact figure for WD "Red"? Their data sheet shows MTBF in hours, not unrecoverable read error rate in bits)

 

[underpickled]

<raising hand> I'm planning exactly that. I figured it was more efficient to use additional drives for off-line backups than for more stripes. The chance of a read-error during rebuilding is related to the amount of data stored, not the entire HDD size. So if I'm only storing 1.5TB of data for now, it doesn't matter that my drives could hold more. The comments on the infamous post push back on the extreme conclusion. Also, newer drives have better failure rates. (Anyone know the exact figure for WD "Red"? Their data sheet shows MTBF in hours, not unrecoverable read error rate in bits)

The MTBF is great, but probably more relevant are the load/unload cycle ratings (both are in the datasheets on WDs website). True, backups are still helpful and effective in case a resilvering breaks another drive. It's just important to have a CONOPS for your setup.

Sent from my Galaxy Nexus using Tapatalk 2

 

[cyberjock]

WD Reds give you URE error rates <1x10^14.

http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-800002.pdf

That's your standard URE error rate.

 

[Pnuts]

Hi Pnuts,

Keep in mind only mad men & thrill seekers use raidz1 with 4TB drives.

That Microserver will actually do 8GB DIMMs, look around and you can find a part number for the Kingston kit that has been proven to work.

-Will

I missed this reply because I never got a new reply email about it, but I ended up finding the same information in newegg reviews and ordered 2x 8gb sticks (16gb kit was out of stock).

I would like to thank everyone for replying and providing information to me. I am installing FreeNAS now as I type this.

 

[survive]

Hi Pnuts,

No worries, that's what we are here for.

Be sure to post back with how the system is working out!

-Will