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I use RAID1 - mirror long time. I have beleaved yet, that RAID1 does stripping on read operation for improve the speed.

While migrating form 160GB disk to 3TB mirror, I started the file copy, watching the real speed on mirrored volume as on mirror members. I'm disappointed that all the read concerns the /dev/sdb only while the other member is sleeping. Do somebody know how to force the stripe-read operations on RAID1?

OS Debian Linux 9 Stretch, mdadm, ext3/4

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    Depends on virtually everything used in your config. RAID controller, HDDs/SSDs, cache/nocache, drivers, etc. Don't rely on RAID1 to be faster than a single drive, especially not when using single thread file transfers. Ah, using mdadm, I skipped that. Have a look at this: superuser.com/questions/385519/… or that: serverfault.com/questions/814546/… – Lenniey Oct 18 '18 at 9:22
  • I prepare the test with RAID10 on two disk: mirror1 sdd1 & sde1 in strip with mirror2 sde2 & sdd2. Could it confuse the mdadm raid1 procedure. (?) – schweik Oct 18 '18 at 14:25
  • Which test are you talking about? Careful, mdadm's RAID10 is not the same as other RAID10s (in your case it should be, though), look here. Also: read performance of RAID10 differs quite much from RAID1. – Lenniey Oct 18 '18 at 15:57
  • Thanks for the wiki link, that's what I want to test (far layout). Two disk, two partitions on each, and first mirror, than strip. First strip, than mirror - it looks more dangerous from my point of view. I will share my results, sure. – schweik Oct 19 '18 at 6:05

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