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I have the following drives:

  • Seagate Barracuda ST3200054AS
  • WDC WD20EADS-00S2B0
  • Samsung HD204UI

As far as I understand, the first are ordinary 512 drives while the last is 4096 (Advanced format). Together with a new 2TB drive, I want to create a 6TB RAIDz1 with ZFS in FreeNAS. The new drive must most likely be also Advanced format because the old 512 are becoming rare/expensive.

So I will effectively have two 512-byte-block and two 4096-byte-block drives. What special things must I take care in order to not decrease performance?

When I chose "Force 4096 bytes sector size" in the volume manager, will I make sure that I will get the same performance if all block sizes were equal?

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Would it make more sense to work with similar drive technologies? – ewwhite Aug 8 '12 at 17:58
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What do you mean with "similar drive technologies"? – divB Aug 9 '12 at 12:16

migrated from serverfault.com Aug 8 '12 at 18:03

2 Answers

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there's no performance penalty in aligning a 512 drive on 4096 boundaries. since 4096 is a multiple of 512, the 512 drives will also be aligned on 512 boundaries.

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Hmm, thanks. Do you know that if this is ensured if I choose the "Force 4096 bytes sector size" option in FreeNAS? If I use Linux Software RAID5, is there an option to ensure the 4096 alignment? – divB Aug 9 '12 at 12:15
Yes, your drive will be aligned correctly if you use that option. I don't have enough experience with Linux software raid to answer your other question. – longneck Aug 9 '12 at 13:28
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The biggest performance drop in your description is that you intend to use RAIDZ. RAIDZ is almost always the wrong choice. Mirroring may not be the best in all situations, but mirroring is never the wrong choice.

Given your situation I would very highly recommend mirroring the two 512-block disks and the two 4096-block disks so that you have striped mirrors. You'll have a pool of 4TB in size.

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Well, maybe but otherwise I have too few space. This is not for real-time use but rather for backup purposes. I already have 3x2 TB and I need at least 5TB in total. 4 are too less. Otherwise I would have to buy 4 new drives. Hence RAID5 (or RAIDz1) is the only option for now. Even if I would go for mirror, I'd have the same question/issue – divB Aug 9 '12 at 12:15
Using RAIDZ/RAID5 will likely already impact performance. The additional impact of mixing block sizes probably won't make a noticeable difference at that point. Just feed them all to ZFS and let it worry about the rest. – bahamat Oct 8 '12 at 22:17

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