Re: Good SAS adapters for 6 Gb/s SATA SSD's (with TRIM)?

[Ric Wheeler <ricwheeler@gmail.com>]

On 08/12/2011 09:04 AM, Prof. Dr. Klaus Kusche wrote:
> On 2011-08-12 05:19, Douglas Gilbert wrote:
>> On 11-08-11 03:59 PM, Douglas Gilbert wrote:
>>> On 11-08-11 11:18 AM, Prof. Dr. Klaus Kusche wrote:
>>>> I'm looking for ways to hook up fast 6 Gb/s SATA SSD's (non-RAID!)
>>>> to (server or i-X58) mainboards which do not have native 6 Gb/s SATA.
>>>>
>>>> From the reviews I've read so far, two things became obvious:
>>>> * The SSD's I'm looking at really want a working SATA TRIM command.
>>>> * All the onboard Marvell 88SE9128 (or ASmedia) solutions
>>>> seriuosly lack performance, as do PCIe cards based on those chips.
>>>>
>>>> So basically, there seem to be two choices:
>>>> 1.) LSI 2008
>>>> 2.) Marvell 9485
>>>>
>>>> 1.) seems to be fast, reliable and well-supported,
>>>> but as far as I can tell, it doesn't support TRIM at all:
>>>> It neither maps SCSI unmap to SATA TRIM,
>>>> nor accepts TRIM as a SATA passthrough command.
>>>>
>>>> Is that true?
>>>
>>> What counts in Linux for "trim" support on a SSD (SATA,
>>> SAS or FC) is correctly processing the SCSI WRITE SAME (16)
>>> with the UNMAP bit set. In the case of a SATA SSD, a SCSI
>>> to ATA Translation Layer (SATL) should map that SCSI WRITE
>>> SAME (16) with the UNMAP bit set to the ATA DATA SET
>>> MANAGEMENT command with the TRIM attribute set.
>>>
>>> Many Linux SATA low level drivers use libata which
>>> implements the above mapping. However some SAS HBAs
>>> (e.g. LSI MPT Fusion 3 and 6 Gbps) implement the SATL
>>> in their own HBA firmware.
>>>
>>> I tested a LSI SAS 9212-4i4e HBA running its most recent
>>> firmware (9.0 from Feb 26, 2011) with a Intel SSDSA2M080
>>> which does support trim. I used my ddpt utility and the
>>> SCSI WRITE SAME (16) with the UNMAP bit set was rejected
>>> as an "illegal request". With the UNMAP bit clear it
>>> accepted the command. I also checked the SCSI UNMAP
>>> command and it was also rejected.
>>>
>>> LSI have some more work to do on their firmware.
>>
>> I did check the LSI support page for my HBA just before sending
>> my original reply. And the version 9 firmware was showing at the
>> top of the list. Alas, that page had been alpha sorted on the
>> file names so that version 10 of the firmware (May 2011) was
>> hiding further down the page :-)
>>
>> So I installed the newest firmware and redid the above tests.
>> Now the SCSI WRITE SAME (16) with the UNMAP bit set works on
>> that SSD. The SCSI UNMAP command was rejected and I did not
>> test sending the ATA DATA SET MANAGEMENT command through
>> the pass-through (but I expect that would work).
>>
>> So Linux file systems will be able "discard" (="unmap"(SCSI);
>> ="trim"(ATA)) data using LSI HBAs based the LSI 2008 chip
>> which are running recent firmware.
>
> Was that with the RAID or the non-RAID firmware?
>
> I've asked LSI sales/support about UNMAP/TRIM being supported.
> They've opened a case, but I got zero response up to now.
> So it doesn't seem to be on the official feature list,
> and it seems to be unknown at least in the Munich LSI office.
>
> Am I correct that this would support online trimming (mount discard),
> but not batch trimming with wiper.sh or similar tools/scripts,
> because they issue TRIM or UNMAP directly, not WRITE SAME UNMAP?
> (what's the SCSI equivalent to the wiper.sh script?)
>
> Nobody having any info's about Marvell / mvsas?
>
> Klaus.
>

Discard issues the same SCSI command regardless of the online versus batch 
operation. If one works, the other should work as well.

Regards,

Ric