Re: What does TRIM/discard in RAID do ?

On 18/01/2023 at 10:57, Reindl Harald wrote:

Am 18.01.23 um 00:26 schrieb Pascal Hambourg:

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in such implementations you have to consider

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* file-systems with no trim-support

Not affected. A device does not need TRIM support to know which 
blocks have been written and contain valid data

well, fstrim/discard don't do anything on a HDD at the FS layer

(Hard disks with SMR technology may support TRIM to avoid useless 
read-modify-write operations, but SMR is not recommended for RAID so it 
is a bit out-topic.)

Not sure I get your point. How is a filesystem with no TRIM support 
related with a hard disk with no TRIM support ?

Currently the RAID layer does TRIM/discard pass-through only, so it 
returns the status of the underlying devices. If it stored information 
about which blocks contain valid data, I guess it would have to 
advertise TRIM/discard support for itself regardless of the underlying 
devices.