Date: Tue, 12 May 2015 16:09:46 +0200 From: InterNetX - Juergen Gotteswinter <jg@internetx.com> To: freebsd-fs@freebsd.org Subject: Re: ZFS RAID 10 capacity expansion and uneven data distribution Message-ID: <555209AA.9010606@internetx.com> In-Reply-To: <5552071A.40709@free.de> References: <5552071A.40709@free.de>
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Am 12.05.2015 um 15:58 schrieb Kai Gallasch: > Hello list. > > What is the preferred way to expand a mirrored or RAID 10 zpool with > additional mirror pairs? > > On one server I am currently using a four disk RAID 10 zpool: > > zpool ONLINE 0 0 0 > mirror-0 ONLINE 0 0 0 > gpt/zpool-da2 ONLINE 0 0 0 > gpt/zpool-da3 ONLINE 0 0 0 > mirror-1 ONLINE 0 0 0 > gpt/zpool-da4 ONLINE 0 0 0 > gpt/zpool-da5 ONLINE 0 0 0 > > Originally the pool consisted of only one mirror (zpool-da2 and zpool-da3) > > I then used "zpool add" to add mirror-1 to the pool > > Directly afer adding the new mirror I had all old data physically > sitting on the old mirror and no data on the new disks. yep, this is the expected result > > So there is much imbalance in the data distribution across the RAID 10. > The effect is now, that the IOPS are not evently distributed about all > devs of the pool and e.g. "gstat -p" when the server is very busy > showed, that the old mirror pair can max out at 100% I/O usage while the > other one is almost idle. right, works as designed > > Also: I also noted that the old mirror-pair had a FRAG about 50%, while > the new one only has 3%. > same here > So is it generally not a good idea to expand a mirrored pool or RAID 10 > pool with new mirror pairs? > depends > Or by which procedure can the existing data in the pool be evenly > distributed about all devices inside the pool? > destroy / recreate > Any hint appreciated. > > Regards, > Kai. >
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