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Ext4 and Discard option (TRIM)
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Zarhan
l33t
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Joined: 27 Feb 2004
Posts: 960

PostPosted: Mon Jul 12, 2010 7:37 pm    Post subject: Ext4 and Discard option (TRIM) Reply with quote

I recently upgraded to X-25 G2 SSD drive from Intel. I've been running ext4. Now, the kernel docs state that

Code:
discard         Controls whether ext4 should issue discard/TRIM
nodiscard(*)            commands to the underlying block device when
                        blocks are freed.  This is useful for SSD devices
                        and sparse/thinly-provisioned LUNs, but it is off
                        by default until sufficient testing has been done.


...sooo, in practice, what does this mean? This is talking about a *filesystem* and I'd sure prefer that I wouldn't get data loss or anything like that, but how "experimental" is this still? What tests have been done and what's the verdict? Should I wait for 2.6.35 or even beyond before setting that option?
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ssteinberg
Apprentice
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Joined: 09 Jul 2010
Posts: 206
Location: Israel

PostPosted: Mon Jul 12, 2010 8:05 pm    Post subject: Reply with quote

Not using an SSD myself yet on home's machine so I can only report what I researched.
TRIM marks an erase block on the SSD as unused (aka free) by the fs. Meaning the next time a write operation takes place on this block the SSD can write without the read->erase->write performance penalty. This is also especially useful for Intel's SSD.
Apparently the TRIM code that comes with the 2.6.34 kernel is still highly unoptimized. Seems like 2.6.35 works well.
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Zarhan
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Joined: 27 Feb 2004
Posts: 960

PostPosted: Mon Jul 12, 2010 8:27 pm    Post subject: Reply with quote

Yeah, I know what TRIM means, but ok, I'll wait for 2.6.35 before turning it on then.
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