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Re: SSD TRIM software raid (mdadm)

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Le 09/01/2019 à 22:22, basti a écrit :
> I have create a software raid level 1 with mdadm.
> 
> One drive is a "classic" HDD.
> The 2'nd drive is a SSD with option "write-mostly".

Why did you flag the SSD as write-mostly ? I would have expected the 
opposite.

> Over the raid I have create and LVM with all the partitions (root,swap
> and qemu/KVM VM's).
> 
> When I understand mdadm the hole space is marked as used.

I don't understand what you mean.

> So my question is how useful is fstrim on /dev/mdx and would it relay
> trim the SSD?

RAID 1 supports TRIM since kernel 3.7. Since the HDD does not support 
TRIM, it will make discarded bloc contents inconsistent between the SSD 
and the HDD but it does not matter.

However you wrote that the RAID device is used by LVM, so you cannot run 
fstrim on it directly. You must enable TRIM/discard in LVM (see 
lvm.conf) and run fstrim on LVs which contain mounted filesystems 
supporting TRIM/discard.

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Thread

SSD TRIM software raid (mdadm) basti <mailinglist@unix-solution.de> - 2019-01-09 22:30 +0100
  Re: SSD TRIM software raid (mdadm) Pascal Hambourg <pascal@plouf.fr.eu.org> - 2019-01-10 01:00 +0100
    Re: SSD TRIM software raid (mdadm) basti <mailinglist@unix-solution.de> - 2019-01-10 10:50 +0100
  Re: SSD TRIM software raid (mdadm) David Christensen <dpchrist@holgerdanske.com> - 2019-01-10 03:50 +0100

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