Question About Disk Capacity Relative To Replacing An Existing Disk

TrueNAS General
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I have a question about actual disk capacity in bytes relative to the TrueNAS disk replacement requirements.

My NAS currently has four Western Digital 6 TB Red Plus drives (model WD60EFZX) configured in RAIDZ2.

According to the TrueNAS documentation, when replacing a failed disk, the replacement drive must be of equal or greater capacity than the original drive.

When I looked for replacement options, I found that the current 6 TB Red Plus has a model number of WD60EFPX instead of WD60EFZX.

My question is:

If I replace a WD60EFZX with a WD60EFPX, could there be a problem that the new model’s exact byte capacity is slightly smaller (even by a few thousand bytes)?

In other words, when a manufacturer says a drive is 6 TB, is that always exactly 6 000 000 000 000 bytes, or does the true capacity vary slightly between models. If it does verify, could that small difference prevent its use as a replacement?

Thank you in advance for any information or thoughts on this question.

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Use drive of the exact same size or larger. It it up to you to count every bit and byte.
It has happened in the past.

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As @SmallBarky says - new drives are sometimes a slightly different size to older drives. (sometimes larger, sometimes smaller)

TN used to create a 2GB swap partition on each drive to take this into account - but IX for some reason took that away (and have been moaned at as a result). My non-scientific reasearch says that this is more likley to occur with SSD’s but thats not exclusive

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As of, I think, 24.10, TrueNAS no longer creates the swap partition, but creates a data partition of ($DISK_SIZE - 2 GB), for this exact reason. If a replacement disk is smaller than an original by less than 2 GB, that difference covers it. If the difference is greater than 2 GB, of course, you’re kind of screwed.

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Thank you to everyone who replied to my original question — the responses were very helpful.

Based on the feedback, it looks like I should be able to use a newer 6 TB Red Plus WD60EFPX drive as long as its actual capacity is no more than 2 GB less than my existing WD60EFZX disks.

I may also extend my RAIDZ2 vdev by adding one or two additional 6 TB WD60EFPX drives. (I need to do some further research on extending a RAIDZ VDEV as there seems to be some caveats.)

I have one quick follow-up question:

When extending, the added drive must be of equal or greater capacity than the existing drives. It is reasonable to assume the same ($DISK_SIZE - 2 GB) tolerance is used to determine if the additional drive is equal or greater in capacity?