Date: Thu, 1 Sep 2011 12:46:12 -0500 From: Daniel Mayfield <dan@3geeks.org> To: freebsd-fs@freebsd.org Subject: Re: gptzfsboot and 4k sector raidz Message-ID: <553883C7-B97D-429F-AF4A-E208B6051B62@3geeks.org> In-Reply-To: <4E5FBE3E.7020706@snakebite.org> References: <F335600A-0364-455F-A276-43E23B0E597E@3geeks.org> <4E5F811A.2040307@snakebite.org> <7FAD4A4D-2465-4A80-A445-1D34424F8BB6@3geeks.org> <4E5FBE3E.7020706@snakebite.org>
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>> I noticed that the free data space was also bigger. I tried it with >> raidz on the 512B sectors and it claimed to have only 5.3T of space. >> With 4KB sectors, it claimed to have 7.25T of space. Seems like >> something is wonky in the space calculations? >=20 > Hmmmm. It didn't occur to me that the space calculations might be = wonky. That could explain why I was seeing disk usage much higher on 4K = than 512-bytes for all my zfs datasets. Here's my zpool/zfs output w/ = 512-byte sectors (4-disk raidz): >=20 > [root@flanker/ttypts/0(~)#] zpool list tank > NAME SIZE ALLOC FREE CAP DEDUP HEALTH ALTROOT > tank 7.12T 698G 6.44T 9% 1.16x ONLINE - > [root@flanker/ttypts/0(~)#] zfs list tank > NAME USED AVAIL REFER MOUNTPOINT > tank 604G 4.74T 46.4K legacy >=20 > It's a raidz1-0 of four 2TB disks, so the space available should be = (4-1=3D3)*2TB=3D6TB? Although I presume that's 6-marketing-terabtyes, = which translates to ... 6000000000000/(1024^4)=3D5. And I've got 64k = boot, 8G swap, 16G scratch on each drive *before* the tank, so eh, I = guess 4.74T sounds about right. >=20 > The 7.12T reported by zpool doesn't seem to be taking into account the = reduced space from the raidz parity. *shrug* >=20 > Enough about sizes; what's your read/write performance like between = 512-byte/4K? I didn't think to test performance in the 4K = configuration; I really wish I had, now. I didn't test performance. I'm doing all the work running from the = mfsBSD boot disc. I'm not sure a simple 'dd' is a good test, but if you = have suggestions, I'm open. daniel
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