Messages in this thread | | | Date | Thu, 20 Aug 2009 10:42:09 -0400 | From | Ric Wheeler <> | Subject | Re: [PATCH, RFC] xfs: batched discard support |
| |
On 08/20/2009 10:38 AM, Mark Lord wrote: > Ric Wheeler wrote: >> >> Note that returning consistent data is critical for devices that are >> used in a RAID group since you will need each RAID block that is used >> to compute the parity to continue to return the same data until you >> overwrite it with new data :-) >> >> If we have a device that does not support this (or is misconfigured >> not to do this), we should not use those devices in an MD group & do >> discard against it... > .. > > Well, that's a bit drastic. But the RAID software should at least > not issue TRIM commands in ignorance of such.
If the storage can return different data in a sequence of READ requests of the same sector (with no writes), there is nothing RAID could do. It would see total garbage...
> Would it still be okay to do the TRIMs when the entire parity stripe > (across all members) is being discarded? (As opposed to just partial > data there being dropped)
This should be safe if the MD bitmaps would prevent us from trying to READ/regenerate parity for that stripe...
ric
| |