[Info-vax] Solid State Disks - SCSI- work fine on Alpha

[Stephen Hoffman]

On 2013-12-26 23:03:24 +0000, David Turner said:

> I have been playing with SSD (SOlid State Drives) in Alphaserver DS15
> They actually work!!!
> I am assuming that TRIM is built into Alpha OVMS or can be patched with 8.4?

AFAIK, there is no TRIM support in any released version of OpenVMS.   
If TRIM has been implemented, nobody at HP has bothered to mention it.  
That would be somewhat unusual, particularly given the nature of this 
question.

AFAIK, SSD support was added to OpenVMS I64 UPDATE V7.0, but that 
appears to largely comprise the "gas gauge" support that was added to 
check the SSD lifetime and the remaining spares.   This is the "HP 
SMARTSSD Wear Gauge" feature.

TRIM is normally implemented in the file system, as that's the piece 
that knows about what's allocated and what's not.  On OpenVMS, this 
would likely involve changes to the file system (XQP) of OpenVMS.  This 
can also involve the addition of a disk scrubber; a tool that 
overwrites deallocated storage, often checking for errors.  With an 
SSD, this can send the TRIM command to the device.

With Itanium, you'd probably want to have the second-generation 
SAS/SATA P410 or later, as the more common first-generation SAS/SATA 
P400 controller only does 1.5 Gbps SAS/SATA (3 Gbps for SAS), and I'd 
guestimate that three moderately-busy SSDs would saturate the slower 
controller.

In general, OpenVMS Alpha doesn't really have the speed to take 
advantage of SSD.   The Alpha boxes and the older PCI-X buses just 
aren't that fast.  (Ultra3 SCSI is theoretically in the same 
performance range as the first-generation SATA here, but the devices 
usually found on those buses are much slower.  And SAS and SATA has one 
controller port, where SCSI is shared.  No bus contention with 
SAS/SATA.)

For the operating systems that lack TRIM support, the usual add-on is a 
tool that scans drive free space and sends the TRIM commands, and 
there's at least one third-party tool that claims to provide this for 
OpenVMS.  This tool is analogous to a defragger, but the underpinnings 
of what are happening here do differ very substantially; this is closer 
to a disk scrubber than a defragger.  Even with caching of its previous 
activities, using a scrubber for TRIM is resource-inefficient.

There's an HP OpenVMS I/O Performance presentation that mentions SSD here:
<http://c.ymcdn.com/sites/www.connect-community.org/resource/resmgr/2011_boot_camp_presos2/pre_con_storageio_tipstricks.pdf> 


The OpenVMS Technical Journal (VTJ) SSD article, though with no mention 
of TRIM support:
<http://h20195.www2.hp.com/V2/GetPDF.aspx/4AA4-4794ENW.pdf>

Some more general HP reading on ProLiant SSD support and features:
<http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01071496/c01071496.pdf> 

<http://h18004.www1.hp.com/products/servers/proliantstorage/serial/sata/statedrive/index-g2.html> 


Not sure what of the above documentation is still considered current 
and supported.

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