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   Tom :damnified: (thomas@metalhead.club)'s status on Friday, 07-Apr-2023 02:53:21 JST Tom :damnified:

   Dear storage experts and #mastoadmin s on #Mastodon

   I'm not sure about my storage configuration and could need some assistance.

   I have two NVMe SSDs in software RAID-1 via mdadm. Then LUKS on top. Then LVM on top.

   While raw disk performance is about 2,4 GB/s, only about 900MB/s will be available when reading from one of the LVM volumes.

   It seems like RAID-1 is not doubling the read speed and LUKS has big performance impact.

   Am I missing alignment stuff?

   Notes: https://haste.tchncs.de/raw/xodakomiru

   • Embed this notice
     Albert ARIBAUD ✎ (aaribaud@mastodon.art)'s status on Friday, 07-Apr-2023 02:53:19 JST Albert ARIBAUD ✎

     in reply to

     @thomas

     RAID-1 is not supposed to double the read speed; RAID-0 is (roughly speaking).

     Are you looking for speed or are you looking for reliability?

   • Embed this notice
     Tom :damnified: (thomas@metalhead.club)'s status on Friday, 07-Apr-2023 02:53:20 JST Tom :damnified:

     in reply to

     I'm missing experience in this topic, but only getting half the read speed despite running _two_ NVMes looks odd to me. There must be something wrong ... I'd be very happy if you could guide me into the right direction :)

     Maybe the default values for alignment are not okay. Maybe I'm missing something. How can I check whether everything is fine?

   • Embed this notice
     Albert ARIBAUD ✎ (aaribaud@mastodon.art)'s status on Friday, 07-Apr-2023 03:06:24 JST Albert ARIBAUD ✎

     in reply to

     @thomas No idea regarding mdam, sorry.

     Reliability, so RAID 1 is the right mode.

     RAID 1 reads are performed by any one of the disks.

     So two sequential reads will be performed sequentially anyway, so, as fast as a single disk at best, and possibly worse because of the added layer of disk management.

     Now, two *simultaneous* reads (e.g. two files read in parallel) may be serviced by one disk each, and *may* be faster, even with the management overhead.

     Hope this clarifies.

   • Embed this notice
     Tom :damnified: (thomas@metalhead.club)'s status on Friday, 07-Apr-2023 03:06:25 JST Tom :damnified:

     in reply to

     • Albert ARIBAUD ✎

     @aaribaud ooh I didn't expect that. For me it makes sense that data can be read from two sources simultaneously (RAID-1, mirror). ? Thus, double the read speed.

     I'm looking for reliability.

     But it seems like there are limitations. Reading a _single_ file won't be faster.

     Does RAID1 increase performance with Linux mdadm? - Super User - https://superuser.com/questions/385519/does-raid1-increase-performance-with-linux-mdadm