作者: nchiu 時間: 2012-3-25 23:06 標題: NAS用嘅Hard Disk選擇
其實現時NAS用什麼HD好！？以行Raid 1或 5計，用5900轉嘅節能HD如Seagate或WD嘅green系列會唔會發揮唔到NAS嘅應有效能！？
Thanks！！
作者: lauyincheung 時間: 2012-3-25 23:22
本帖最後由 lauyincheung 於 2012-3-25 23:24 編輯
回復 1# nchiu
Depends on the class of NAS you use. You can check online for the throughput for both the NAS and HDD and find out where the bottleneck is. You can look on the manufacturer claims for NAS and HDD benchmarks on site like hothardware for some idea.
作者: nchiu 時間: 2012-3-26 00:11
回復 2# lauyincheung
Thanks for for advise, I have read the throughput of the NAS & harddisk already. but the point is, I still don't know how to estimate how the performance affected under the raid conditional. Say DS412+, the offical throughput of Raid 5 w/o Link Aggregation is around 110MB/s (large file transfer test). So under Raid 5 condition, what is the min. requirement of the sustained transfer rate of a HD to achieve 110MB/s? I really have no idea. Could you pls help & guide me how to figure it out on Internet. Thanks very much!
作者: 病態賭徒 時間: 2012-3-26 00:16
i want 4TB... but green version is not good for raid mode?
作者: nchiu 時間: 2012-3-26 00:32
回復 4# 病態賭徒
my thought is... Green version won't made the NAS unstable, but will it made the Raid performance slower? if yes, what is the percentage in performance drop? coz reference to the Synology site, they use enterprise level HD to perform the test. the reason to use enterprise level HD is... (Synology use WD2003FYYS 2TB for raid 5 test in which the benchmark of this WD is around ~110MB/s throughput in average)
(1) make the bottleneck fall back to the NAS perfomrnace itself? or...
(2) need to use enterprise level to perform such good testing result (this means the NAS perfomance faster than HD throughput)
so... what if I use a green edition to build my Raid 5 in DS412+??
作者: lauyincheung 時間: 2012-3-26 00:54
本帖最後由 lauyincheung 於 2012-3-26 00:58 編輯
回復 5# nchiu
http://www.tomshardware.com/charts/hard-drives-and-ssds,3.html
There are harddisk chart for 2012 and also RAID 0 however it doesnt have on for RAID 5. According to wikipedia,The read performance of RAID 5 is almost as good as RAID 0 for the same number of disks. So maybe the RAID 0 chart is still good for some sort of comparsion. Even know it may not have the exact model you are using, but it can give you a rough estimate.
References
http://en.wikipedia.org/wiki/Standard_RAID_levels
http://www.tomshardware.com/charts/hard-drives-and-ssds,3.html
作者: 永恆的回憶 時間: 2012-3-26 01:23
本帖最後由 永恆的回憶 於 2012-3-26 01:28 編輯
Accessing data from a RAID-5 array is as good as RAID-0, ie. theoretically multiple that on single disk, but the write performance is still slow because of generating checksum data, but it should still always reaches >100MB if you use at least an Atom CPU.
Also, apart from sequential speed, which may be trivial due to GbE limitation, seek time is also a determining factor affecting your overall RAID performance. HDDs with higher rotational speed could have a lower random seek time.
You could plan how much space you will probably fill up in your array first, before deciding which harddisk model you will buy, because when data is getting more and more, you may reach the zone over the inner circle of your harddisk, and its speed is just below the half of its maximum speed (by single disk). Disks with higher rotational speed will also more significantly benefit in such situation.
Whichever models of rotational speed you will choose, just remember to avoid WD Green (Seagate 5K4 by the way is of no problem) because its rotational speed is variable and will most probably cause the RAID to degrade unexpectedly.
作者: nchiu 時間: 2012-3-26 02:02
本帖最後由 nchiu 於 2012-3-26 02:29 編輯
回復 7# 永恆的回憶
Thanks for your valuable info. That's why I am using seagate LP 2GB on my old 207+ instead of WD. Actually I planned to upgrade my NAS to 412+. Now I'm thinking use my old Seagate LP 2GB on 412+ and add one more LP to build a raid 5 disk array or should I upgrade all HD to 7200rpm if have more than 10% performance gain compared with LP. Any idea and suggestion on my case!?
作者: sinister6 時間: 2012-3-26 11:36
I have 2x WD RE4 1T in my DS209, also considering to upgrade to 412+
the question for now is to buy 2 more 1T RE4 or change to cheaper (i.e Black, Green) 2/3T HDD.. hard decision..
作者: Livermore 時間: 2012-3-26 11:46
回復 7# 永恆的回憶
it seems that the WD green drives don't actually seem to vary their rotational speed (at least, the drive marked as "IntelliPower"), please read http://www.seagate.com/docs/pdf/ ... lipower_exposed.pdf
作者: nchiu 時間: 2012-3-26 12:24
本帖最後由 nchiu 於 2012-3-26 12:30 編輯
I have 2x WD RE4 1T in my DS209, also considering to upgrade to 412+
the question for now is to buy ...
sinister6 發表於 2012-3-26 11:36
here is my thought... reference to the spec. quote officially, the max read/write rate of Raid-5 array with Link Aggregation enabled is;
每秒 205.68 MB 以上的讀取速度、每秒 182.66 MB 以上的寫入速度
assume to achieve the captioned speed, a high end enterprise level HD must be used. if we changed to use a GREEN power HD, assuming the max transfer rate of Raid-5 array would drop around 30%, we still got 140MB/s & 127MB/s with Link Aggregation enabled.
On one hand, if we don't use Link Aggregation (its too expensive for a managed switch on my home network). the max throughput would be limited by 1Gbps LAN speed. theorodically is 125MB/s & 125MB/s (up/down). still lower than 140 & 127MB/s.
Conclusion: No significant perfomance drop in case u DON'T enable Link Aggregation. But the response & seek time will slower as your GREEN HD only got 5900rpm compared with 7200rpm HD.
p.s. above just my own thought (not sure is correct or not) & please feel free to comment & discuss
作者: lauyincheung 時間: 2012-3-26 22:14
本帖最後由 lauyincheung 於 2012-3-26 22:27 編輯
回復 1# nchiu
The latency bottleneck usually lies between the network instead of the HDD. This would usually add another 2-4 ms to your original 10ms latency so the latency on the hdd isnt really an issue. typical dealy on a good switch is 7 microseconds on 100Mbps mode and 3 microseconds on 1000Mbps mode. These values are just for reference and i dont think it will affect your daily use.
This is just like linking to google take around 20-30ms but you dont really realise the minor dealys.
I think if the rest of you hardware support it, you should invest into a 8 or 16 port managed switch. I think they should cost around 1-2k and its worthwhile if you are already spending so much on your other hardware as well as the fact that some companies provide livetime next business day warranty. So its "expensive to buy, but cheap to use"
作者: sinister6 時間: 2012-3-27 01:07
well yes but 4x 1T with raid 5 wont take long to fill up. used 1.6T in jbod at the moment, then i may need to buy another 4 HDDs..
作者: greatzelda 時間: 2012-3-28 13:51
用緊2隻3T green版raid 1冇問題