diff --git a/drivers/scsi/sd.c b/drivers//scsi/sd.c
--- a/drivers/scsi/sd.c 2013-09-14 12:53:21.000000000 +0400
+++ b/drivers//scsi/sd.c 2013-12-19 21:43:29.000000000 +0400
@@ -137,6 +137,7 @@
char *buffer_data;
struct scsi_mode_data data;
struct scsi_sense_hdr sshdr;
+ static const char temp[] = "temporary ";
int len;
if (sdp->type != TYPE_DISK)
@@ -144,6 +145,13 @@
* can do it, but there's probably so many exceptions
* it's not worth the risk */
return -EINVAL;
+
+ if(strncmp(buf,temp,sizeof(temp) - 1 ) == 0) {
+ buf += sizeof(temp) - 1;
+ sdkp->cache_override = 1;
+ } else {
+ sdkp->cache_override = 0;
+ }
for (i = 0; i < ARRAY_SIZE(sd_cache_types); i++) {
const int len = strlen(sd_cache_types[i]);
@@ -157,6 +165,13 @@
return -EINVAL;
rcd = ct & 0x01 ? 1 : 0;
wce = ct & 0x02 ? 1 : 0;
+
+ if(sdkp->cache_override){
+ sdkp->WCE = wce;
+ sdkp->RCD = rcd;
+ goto out;
+ }
+
if (scsi_mode_sense(sdp, 0x08, 8, buffer, sizeof(buffer), SD_TIMEOUT,
SD_MAX_RETRIES, &data, NULL))
return -EINVAL;
@@ -174,6 +189,7 @@
sd_print_sense_hdr(sdkp, &sshdr);
return -EINVAL;
}
+out:
revalidate_disk(sdkp->disk);
return count;
}
@@ -1995,6 +2011,9 @@
int old_wce = sdkp->WCE;
int old_rcd = sdkp->RCD;
int old_dpofua = sdkp->DPOFUA;
+
+ if(sdkp->cache_override)
+ return;
if (sdp->skip_ms_page_8)
goto defaults;
@@ -2416,6 +2435,7 @@
sdkp->capacity = 0;
sdkp->media_present = 1;
sdkp->write_prot = 0;
+ sdkp->cache_override = 0;
sdkp->WCE = 0;
sdkp->RCD = 0;
sdkp->ATO = 0;
diff -u a/drivers/scsi/sd.h b/drivers//scsi/sd.h
--- a/drivers/scsi/sd.h 2013-09-14 12:52:43.000000000 +0400
+++ b/drivers//scsi/sd.h 2013-12-19 16:52:25.000000000 +0400
@@ -71,6 +71,7 @@
u8 provisioning_mode;
unsigned previous_state : 1;
unsigned ATO : 1; /* state of disk ATO bit */
+ unsigned cache_override : 1; /* temp override of WCE,RCD*/
unsigned WCE : 1; /* state of disk WCE bit */
unsigned RCD : 1; /* state of disk RCD bit, unused */
unsigned DPOFUA : 1; /* state of disk DPOFUA bit */
On 01/15/2014 08:03 AM, Robert van Leeuwen wrote:Even at that, there has been some concern on the list (and lkml) that certain older Intel drives without super-capacitors are ignoring ATA_CMD_FLUSH, making them very fast (which I like!) but potentially dangerous (boo!). The 520 in particular is a drive I've used for a lot of Ceph performance testing but I'm afraid that if it's not properly handling CMD FLUSH requests, it may not be indicative of the performance folks would see on other drives that do.
Power-Loss Protection: In the rare event that power fails while the
drive is operating, power-loss protection helps ensure that data isn’t
corrupted.
Seems that not all power protected SSDs are created equal:
http://lkcl.net/reports/ssd_analysis.html
The m500 is not tested but the m4 is.
Up to now it seems that only Intel seems to have done his homework.
In general they *seem* to be the most reliable SSD provider.
On the third hand, if drives with supercaps like the Intel DC S3700 can safely ignore CMD_FLUSH and maintain high performance (even when there are a lot of O_DSYNC calls, ala the journal), that potentially makes them even more attractive (and that drive already has relatively high sequential write performance and high write endurance).
Cheers,
Robert van Leeuwen
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