blue_Bandana

Did some thorough research: Pro Price # SATA-Ports HDD-Trays PSU / Case / Mainboard / Ram etc all included Dealer is within 1hour by car Con no fun of building my own server Raidcontroller can not be flashed to HBA-Mode, therefore: HDD's can not be taken off the controller and used on any standart SATA-Port as the Raid-Controller messes with the disks ... which eliminates an (for me) important feature of unRaid upgrading RAM or CPU would be a pure waste of money as Ram: 16 GB of DDR2 fully-buffered ECC RAM costs more than 16GB of unbuffered DDR4-ECC ram I think i will call the dealer and ask about an used case + PSU ... looks like he is into the "refurbished server business" so i will give this a try best regards blue_Bandana

This chance of encountering an UBE is correct if my hypothesis is right, that UBE's can be modelled as a Poisson-Process with rate 10^-14.

I would suggest you take a look at the table at the end of my post and decide yourself how much risk you are willing to take. Explenation of the math: Have a look at your HDD-Specs, you will finde something like "Non-recoverable read errors per bits read", for WD-Red you get "<1 in 10^14". Now think of how many bits have to be read to recover a faild drive (i.e. all bits on all non-failed drives). The closer the number of bits that have to be read is to the error-rate ... the higher the risk in encountering a second "failure" while rebuilding the failed drive. Lets say the "1 in 10^14" is the "expectation" of a Poisson-Process counting the erros you encounter while reading. This process therefore has the rate "10^-14". The probability in not encountering an error while reading 4TB ~ 3.5x10^13 is e^(- 10^-14 * 3.5x10^13) = 0.7047 = 70.47% Now if you have 7x 4TB drives and 1 parity you have to hope for 6 drives not to fail (having read-errors) while being read (for the rebuild). The probability in not encountering an error on all 6 drives is therefore 0.7047^6 = 0.122 = 12.2%. Are you willing to take an 87.8% chance in corrupted data / loosing all your data while rebuilding? Or would you rather pay the premium (buying + occupied SATA-Port + electricity) and have peace of mind? Please remember: no raid is a substitute for a backup For the people who do not want to do the maths: The following table gives the chance of encountering at least one read error. Hypthesis: Such errors can be modeled as Poisson-Process with rate "1/expectation" first line = expected error rate, please consider "<1 in 10^14" could be any value, enterprise disks are typically "<1 in 10^15" so your real value is brobably something in between this table first column = size data to be read while rebuilding 1 expected error in: 1,00E+14 2,00E+14 3,00E+14 4,00E+14 5,00E+14 6,00E+14 7,00E+14 8,00E+14 9,00E+14 1,00E+15 2TB16,13%8,42%5,70%4,30%3,46%2,89%2,48%2,18%1,94%1,74% 4TB29,66%16,13%11,07%8,42%6,79%5,70%4,90%4,30%3,83%3,46% 6TB41,01%23,19%16,13%12,36%10,02%8,42%7,26%6,38%5,70%5,14% 8TB50,52%29,66%20,91%16,13%13,13%11,07%9,56%8,42%7,52%6,79% 10TB58,51%35,58%25,41%19,74%16,13%13,64%11,81%10,41%9,31%8,42% 12TB65,20%41,01%29,66%23,19%19,03%16,13%14,00%12,36%11,07%10,02% 14TB70,81%45,98%33,67%26,50%21,83%18,55%16,13%14,27%12,79%11,59% 16TB75,52%50,52%37,45%29,66%24,53%20,91%18,21%16,13%14,48%13,13% 18TB79,47%54,69%41,01%32,69%27,14%23,19%20,24%17,96%16,13%14,64% 20TB82,78%58,51%44,37%35,58%29,66%25,41%22,22%19,74%17,76%16,13% 22TB85,56%62,00%47,54%38,36%32,09%27,57%24,15%21,49%19,35%17,59% 24TB87,89%65,20%50,52%41,01%34,44%29,66%26,04%23,19%20,91%19,03% 26TB89,84%68,13%53,34%43,55%36,71%31,69%27,87%24,86%22,44%20,44% 28TB91,48%70,81%56,00%45,98%38,90%33,67%29,66%26,50%23,94%21,83% 30TB92,86%73,27%58,51%48,30%41,01%35,58%31,41%28,10%25,41%23,19% 32TB94,01%75,52%60,87%50,52%43,05%37,45%33,11%29,66%26,86%24,53% 34TB94,97%77,58%63,10%52,65%45,02%39,25%34,77%31,19%28,27%25,85% 36TB95,79%79,47%65,20%54,69%46,92%41,01%36,39%32,69%29,66%27,14% 38TB96,47%81,20%67,18%56,64%48,75%42,71%37,97%34,15%31,02%28,41% 40TB97,04%82,78%69,05%58,51%50,52%44,37%39,51%35,58%32,36%29,66% 50TB98,77%88,91%76,92%66,70%58,51%51,95%46,65%42,29%38,66%35,58% 60TB99,49%92,86%82,78%73,27%65,20%58,51%52,95%48,30%44,37%41,01% 70TB99,79%95,40%87,16%78,55%70,81%64,16%58,51%53,68%49,55%45,98% 80TB99,91%97,04%90,42%82,78%75,52%69,05%63,41%58,51%54,25%50,52% 90TB99,96%98,09%92,86%86,18%79,47%73,27%67,73%62,83%58,51%54,69% 100TB99,98%98,77%94,67%88,91%82,78%76,92%71,54%66,70%62,37%58,51% 150TB>99,99%99,86%98,77%96,31%92,86%88,91%84,82%80,78%76,92%73,27% 200TB>99,99%99,98%99,72%98,77%97,04%94,67%91,90%88,91%85,84%82,78% 300TB>99,99%>99,99%99,98%99,86%99,49%98,77%97,69%96,31%94,67%92,86% 400TB>99,99%>99,99%>99,99%99,98%99,91%99,72%99,34%98,77%97,99%97,04% 500TB>99,99%>99,99%>99,99%>99,99%99,98%99,93%99,81%99,59%99,25%98,77% This table was created using google-spreadsheets and http://theenemy.dk/table/ to convert. Case: Double parity If you have double parity, the chance of any read-error on your first n drives being exactly where the second-parity (disk n+2) also encounters an read error is ... really small. Let's just assume you got 4kB of "read-errors", so your second-parity drive has to cover those by reading 4kB, the chance of encountering an error while doing so is 1-e^(-10^(-14)*4*8*1024^1)=0,000000000328= 0,0000000328%. Best regards blue_Bandana

Hi, I am about to build an offsite backupserver for myself. Budget: On the cheap side, if there is a very good reason up to 1000 # Drives: 8 absolute minimum, 10 or 12 would be better expandability: not really, except the number of drives (up to 12) unRAID Add Ons: no Drives: I will not buy drives, I already have 8x 2TB drives Spare parts: None except the 8 drives What I am aiming for: offsite Backupserver with 8-12 HDD's Up and running only once a week offsite --> iKVM like IPMI or ILO is a must have Ram: ECC powerconsumption: does not realy matter price: main decision criteria is "price / 8 HDD's" and "price / max-#-SATA-Ports" Parts should be available in Germany i.e. available on the site www.geizhals.de performance: Initial backup will be using 1Gbit/s Network. In the offsite location connection speeds are: 10Mbit/s write, 40Mbit/s read. In other words: Performance does not really matter but double-parity is a must Drives: I will start with 8x 2Tb drives I currently use for backup. I will add/buy mor drives as I run out of space up to the number of SATA-ports and HDD-mounting-points. Then I will start swapping drives for bigger ones. Case size: Does not matter Hot-swap / cold-swap: Not needed. At this moment I have two setups in mind: ASRock-Rack C2550D4I 12x SATA 4x 2,4GHz (2,6GHz boost) 16 GB Ram Fractal Design Node 804 - 10x3.5"HDD ~ 510 € + PSU + Sata-Cabels + Fans or Supermicro X11SSM-F (8x SATA, socket 1151) Pentium G4500 (2x 3,5 GHz, no hyper-threading, no turbo-boost) 16 GB Ram Fractal Design Node 804 - 10x3,5"HDD ~ 462,80 € + SATA-expansion-card + PSU + Sata-Cabels + Fans Possible better CPU's for the last build would be: I3-6100 (2x 3,7GHz, hyper-threading, no boost) +44€ I3-6320 (2x 3,9GHz, hyper-threading, no boost) +98€ E3-1220 V5 (4x 3GHz, no hyper-threading, 3,5GHz boost) +146€ E3-1230 V5 (4x 3,4GHz, hyper-threading, 3,8GHz boost) +207€ E3-1270 V5 (4x 3,6GHz, hyper-threading, 4GHz boost) +289€ but to be honest, I see no reason to go for a better CPU. Do you see a reason to go for a better CPU? What is your oppinion on my first two thoughts? Do you have other recommendations for an "as cheap as possible ~10 Drives in unRaid" build? I would really appreciate your comments, best regards blue_Bandana