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Gaia
Asked: 2019-12-04 10:22:40 +0800 CST

RAID 1 Reliability: 4 drives vs 2 Drives + 2 Spare Drives

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Which is likely to be more reliable (safer data + lower downtime):

having 4 drives in RAID 1 OR having 2 drives in RAID 1 plus 2 spare(s)?

In other words, is there an advantage in having spares when you are setting up RAID 1 with 4 drives?

Background: this is MDADM raid on a current stable Linux distribution. Disks are enterprise grade. Partition in RAID 1 is the root partition (minimal writes), so write performance is not a problem. Hardware allows for hot swapping HDDs. On another partition of the same 4 HDDs I have RAID 10 running for write intensive applications.

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1 Answers

  1. Best Answer

    If by "having 4 drives in RAID" you mean having 4-way RAID1 (ie: 4 duplicate copies of each write), well, this is surely more durable/resilient then a 2-way RAID1 + 2 spares:

    • with 4-way RAID1 all 4 disks need to fail to lose data;
    • with 2-way RAID1 + 2 spares you only need to lose the wrong two disks to lose data (ie: disk #1 fails and, during rebuild, the increased stress kills disk #2)

    That said, 4-way RAID1 is generally overkill for large data partition (3-way mirrors tend to be the upper limit used in the wild). However you can use it for simpler setup and/or peace of mind for smaller dataset as /boot and /.

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