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This is a homework. We are supposed to pick HDD, imagine we are buidling RAID to handle 800 random blocks per second (550 reads/250 writes).
I have picked RAID5 made out of 3 HDDs. But it is too slow.
- 8KiB block size (8192 bytes)
Access time 16ms (benchmarked my WD Caviar)
transfer rate 142MB/s (benchmarked my WD Caviar)
1 block from 1 HDD at 142MB/s = 8192B/142MBps = 0.05769 ms
= 16+0.06 = 16.06 = 16ms
Writting data 2*16ms (data+parity) = 32ms
So for 550reads+250writes it is 550*16 + 250*32 ms = 16.8s
Are my calculations off or is the RAID configuration wrong? Could you point me in a right direction? What RAID config do you recommend?
Ok, I have managed with RAID10 made from 4+4 10k RPM HDDs.
rluks
Posted 2015-04-04T15:46:39.347
Reputation: 399
Both! You forgot the read part of the parity and getting 800IOPS from 3xWD Caviar in RAID5 belongs in a category of 3 days ago. – Eugen Rieck – 2015-04-04T15:49:55.930
Coud you point me in a right direction? – rluks – 2015-04-04T16:11:00.263
If it is homework, then you shouldn't be asking others to do it for you. – psusi – 2015-04-05T01:02:48.633
Just give me a hint. How can I make it handle 800 random blocks per second when 800*16ms > 1s? – rluks – 2015-04-05T07:47:47.073
If you found an answer to your question, please add it as an actual answer. And while you’re at it, why not include the calculations as well? ;) – Daniel B – 2015-04-12T13:33:48.167