Home » Computer » Linux 下 RAID1 的 SSD 會有讀取不平均問題

在「Unbalanced reads from SSDs in software RAID mirrors in Linux」這邊看到作者看 S.M.A.R.T. 數據時發現兩顆 SSD 硬碟組成的 RAID1 有很明顯的讀取不平均的問題:

242 Total_LBAs_Read [...] 16838224623
242 Total_LBAs_Read [...] 1698394290

原因是因為 Linux 對 RAID1 的 SSD 有不一樣的演算法:

The current state of RAID1 read balancing is kind of complex, but the important thing here in all kernels since 2012 is that if you have SSDs and at least one disk is idle, the first idle disk will be chosen.

2016 時演算法就更激進了,變成非 SSD 會:

In kernels with the late 2016 change, this widens to if at least one disk is idle, the first idle disk will be chosen, even if all mirrors are HDs.

加上 SSD 很快,這造成 loading 幾乎都在第一顆上... 這對 SSD 應該是還好啦 (理論上 SSD 的讀取不傷壽命),不過還是有點怪就是了。

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