Subject: Re: bug#51427: [PATCH] nix: libstore: Do not remove unused links when deleting specific items.

From: Felix Lechner <[email-masked]>
Date: Mon, 12 Jun 2023 13:55:46 -0700

Hi,

> Liliana, is your hard disk old or low-end?

Some of my equipment is very old (2011). I think Liliana's issue is
elsewhere. Maybe it's a problem with the DMA setup or with a shared
interrupt. (Dmesg might help.) Liliana, have you tried removing that
rebellious graphics card?

A good place to start when looking at hard drive speeds is the read
performance with

  hdparm -Tt /dev/sdX

I would further look at the tuning parameters of the file system. I
would also try a different internal data cable. (It would be the
connector that has issues.)

For the Guix REPL exercise looking at the links in the store, I
locally got the following results on a mirrored array with two disks
(ext4 on SATA 6 Gb/s, 7200 rpm):

  ;; 70.719509s real time, 14.560439s run time.  3.645179s spent in GC.

On another piece of equipment with three mirrored disks (ext4 on SAS 6
Gb/s, 7200 rpm) I saw:

  ;; 56.528064s real time, 20.906853s run time.  5.087733s spent in GC.

Arrays with multiple drives are sometimes faster because they can read
in parallel.

Kind regards
Felix