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One of the drives failed in my server configured with RAID 5, and I can't find a exact replacement. From my understanding, RAID 5 supports drives with different sizes. Is this safe? Any recommendations, like choosing the same manufacturer or something like that?

RAID 5 in my server is provided by a LSI controller.

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5 Answers 5

up vote 2 down vote accepted

I would always try to stay as similar as possible, so I suggest you to buy from the same manufacturer and hard drive family if possible. Just buy a bigger one.

If not possible, then sure another manufacturer would do it, as long as the disc is exact the same size or bigger, never smaller! Be careful, just being one sector smaller than your old discs will make it not work if your RAID uses the full old disc size. That's why it's recommended while creating a RAID array not to use the whole disc size, but leave some percentage unused, then it's simpler to use different disc with "same" size which have not exact equal sector count.

I have myself some mixed RAID6, Seagate and Hitachi, no problems. But it's not a LSI controller, it's an Areca one.

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You can usually replace a failed RAID member with a larger drive, but not a smaller drive. The RAID will only use the space equivalent to the smallest drive in the array. You can also usually replace a failed RAID member with a drive that runs at a different speed than the other array members.

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+1 concise answer that covers: what if my drive is different size/speed. –  Trevor Boyd Smith Sep 23 '11 at 16:48

its safe to use any other drive as long as its to same or better spec than the old drive, that means same spindle RPM (or better), same interface spec (eg SataII) and same capacity or higher.

i would actually recommend different drive manufacturers as well as different batch numbers of the same drive make/model this just reduces the odds of multiple drive failure at the same time even further

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As long as the drive is large enough to fit the RAID volume then you will be OK, although sometimes different models of drives that are nominally the same size can have slightly different capacity.

This is one of the reasons that 'enterprise' drives all tend to come in standard sizes. Disk array (especially SAN) vendors will source drives from multiple different manufacturers and treat them as interchangeable parts. They will even use disks of different generations (e.g. arrays with mixed ST373405FC and ST373607FC drives) and cripple the firmware in larger drives to make spare parts for arrays with smaller drives when the manufacturer ceases producing drives of that capacity.

You should be able to put a different drive of approprite specification (it can be larger) into the array.

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You "can" use a different HD as mentioned by many above, but let's not just talk about what is acceptable, but instead give best practices answers....

RAID 5 will work with variables, yet best practices have shown that marriaging the exact specifications right down to the batch in Hard Drives seems to offer the highest quality RAID. From both a "performance" standpoint and "quality" RAID configuration.

So work your way backwards from this configuration when replacing a drive. Can't find same batch number, same model number, same size, same manufacturer, etc...

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