[轉載] RAID1: Hardware raid card 不如 onboard

Does HardWare RAID-1 is faster then Linux SoftWare RAID-1 ?
http://forums.gentoo.org/viewtopic-t-750347.html

Post#8 from site admin
I would expect raid1 on a plug in hardware raid card to be slower than kernel raid using the on board SATA connectors.
The key here is 'on board'

The CPU overhead in raid1 is almost zero, as no redundant data is calculated but writes have to det up to both drives, which is just setting up the DMA controller, thats just a few extra bytes for the CPU to write.

The on board SATA interfaces can be operated much faster than the 33MHZ PCI Bus and the reality is, that with a plug in card, the limiting factor becomes the bus bandwidth. The situation is slightly different with a raid5 card, as the redundant data calculations are offloaded from the main CPU but a multi core CPU should not need that sort of help.

If you have a PCI-E raid card, the bus is faster but there are almost no savings to be had for raid1. With this sort of motherboard, your SATA interfaces may be spread over several buses too, so you need to take that into consideration when you do the arithmetic.

In short, you will see no benefit from a hardware raid card working in raid1.

撞鬼 intel atom 主板只有 sata x2

其實仲有一樣野
有d 所謂 raid card 係 fake raid 黎
所以效能同 software 的相近
http://linux-ata.org/faq-sata-raid.html

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我有另一個問題,如果用Linux software RAID (mdadm)的話,
起左RAID5果個array,可唔可以成批由一部機轉去第二部機然後mount番呢?

因為BIOS/hardware raid card我concern既係,如果controller死,成批碟就無得讀...
但如果用Linux software RAID的話,是否會較flexible嘀?

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原帖由 tingcrab 於 2009-6-4 17:25 發表
我有另一個問題,如果用Linux software RAID (mdadm)的話,
起左RAID5果個array,可唔可以成批由一部機轉去第二部機然後mount番呢?

因為BIOS/hardware raid card我concern既係,如果controller死,成批碟就無得讀...
但如果用Linux software RAID的話,是否會較flexible嘀?

yes you could just plug in the drives to another GNU/Linux machine and they would work fine.  This is definitely one of the advantages of using Linux soft RAID.

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My guess assumption:

Hardware RAID 1 - pass write one write request to RAID controller. RAID controller automatic duplication write data to drive 0 and drive 1.

Software RAID 1 - pass two write request to drive 0 and drive 2.

Two write I/O request for Software RAID 1 rather than 1 write I/O for Hardware RAID 1.

Software RAID is very expensive for I/O.

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原帖由 computer1975 於 2009-6-4 19:28 發表
My guess assumption:

Hardware RAID 1 - pass write one write request to RAID controller. RAID controller automatic duplication write data to drive 0 and drive 1.

Software RAID 1 - pass two write requ ...


所以我第時就要試睇下粒3250eU夠唔夠力行RAID5,用CPU代工,對於home server黎講,性價比係好過一隻全hardware以代替RAID工作的card...

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多謝 #4 提供詳盡比較及分析

消化一下之餘,hardware RAID1 expensive 程度幾錢左右? 係唔係有 BBU (Backup Battery Unit) 保護?

自己未用過所謂 fakeRAID, 覺得佢係因應 Windows 先會存在,而 Windows 既野好賣既話就乜都會有。

Quote 之中的 "onboard is the key" 不作準嗎,謝謝。

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強米王

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