3.5in SAS flash drive for R900?
tim at seoss.co.uk
Fri Sep 10 04:53:44 CDT 2010
On 09/09/10 18:57, Philip Tait wrote:
> Will the PERC-6i do TRIM passthrough? If not, you'll need to use an
> AHCI controller such as the server's onboard Intel SATA controller
> (this is what we are using).
> Does your kernel and filesystem support TRIM too?
> Is the availability of TRIM support critical to the operation of these
I believe all SSDs will suffer degraded performance over time, and/or
excessive wear without TRIM - they end up doing extra writes in order to
(unnecessarily) preserve the contents of deleted logical blocks. Same
goes for running them pretty-much full all the time with TRIM. However
the Intel drives suffer less from a lack of TRIM support than some other
designs do (i.e. performance degrades, but doesn't drop through the floor).
This is basically due to the current generation of SSDs pretending a
hard disk - when really they are flash (which has some very different
physical properties). Probably the best solution from an engineering
point of view would be to use a flash-file-system (Linux has several -
and they are designed to suite the physical properties of flash
storage), and have the SSDs expose the raw underlying flash. This
however, is not the route the industry is taking.... TRIM is a piece of
gaffer/duct-tape to fix this problem by providing a mechanism for the OS
to tell the SSD which logical blocks it no-longer needs to work to
Without TRIM a workaround is to periodically discard all data by doing
an ATA security-erase-unit, but this might not fit in with your
bcache also looks very interesting, but is currently alpha-quality
BTW, the machine I'm using currently uses TRIM with both ext4, and btrfs
on an Intel SSD, with an AHCI controller (Intel ICH10).
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