ULINK Analytics: SATA HDD Rankings by Long Latency Reads

Have you ever opened a local file on your computer system that seemed to take a long time to open? If a file takes too long to open, you might quit the opening application and try to open the file again. And if this happens on a regular basis, you might even consider getting a new computer or new drives. This may happen even if your read IOPS, a common indicator of drive speed, is relatively high.

However, chances are that this kind of frustrating user experience willbe reflected in something called long latency read count. Behind the scenes, whenever your system sends a request to read data from your drive, it keeps track of the amount of time that the drive is taking to return that information to the system. If the read request takes longer than a certain amount of time, the system will increment the long latency read count. For HDDs, the criterion for incrementing long latency read count is typically when a read command takes longer than 1000ms + (the number of sectors being read / 256)*2ms.

Long latency reads on an HDD are usually caused by excess read retries. These excess retries can be due to one of two reasons: bad sectors, and badly written data. Bad sectors, or damaged disk media, can be caused by defects that happen during the manufacturing process, or after the manufacturing process by loose particles or head crashes. Data may be badly written if the write was weak, written off-track, or overwritten by data belonging to an adjacent track, which may be caused by vibration. These two reasons usually cause the drive to retry the read several times, possibly with slightly altered head positions or electrical strength. And because each retry requires the head to make another rotation, the read may require several rotations, and thus a longer time, to succeed.

The Importance of Long Latency Read Data in Drive Health Prediction

Furthermore, during the training of our own machine learning algorithms for ULINK DA Drive Analyzer to predict the remaining useful life of drives, we noticed that long latency read data was given high importance scores by the algorithms. This meant that the algorithms determined that long latency read data was useful in predicting drives’ remaining useful life, especially in conjunction with other predictors.

Due to the likely reflection of a slow user experience on this metric and the relationship between this metric and the lifespan of drives, we thought it might be interesting to compare some drive models by their long latency read data to see which ones fared better or worse.

The Data Collection Process

The data we used to rank drive models was SATA HDD health data collected from NAS users in May of 2023. We used drives that had at least two adjacent days of data within that month. For each drive, read command counts were originally reported as lifetime running totals, so we converted these to daily values by calculating daily differences. Long latency read counts were originally reported as daily values and were kept as such. 

Furthermore, we excluded drives with no model info. We excluded drives with non-ASCII model info. We excluded drives that did not report long latency read info or read command count info. We excluded drives that were not issued any read commands. We retained drives that had a power-on year value between 4 and 5 years, because we were interested in ranking drives after they had been used for some time, and because we wanted to control for the possible confound of drive age on rankings. 

For each drive, we calculated the ratio of long latency reads to read commands, and excluded drives whose ratios were outliers (i.e., 1.5 IQR above Q3). This was done so that we could compare the typical user experience between drive models. We retained drive models with at least 100 drives. For each drive model, we then calculated the ratio of total long latency reads to total read commands, and then multiplied the resulting figure by 1 million. This ratio, the “long latency read ratio,” was used to rank the drive models. This left us with 120 drive models and 135,501 drives for ranking.

Table 1: Disk Drive Long Latency Read (LLR) Rankings (for 4 year old drives)

Rank	Mfg	Model Number	Cap(TB)	Drive Count	Avg POY	Total LLR Count	Total Read Cmds (Million)	LLR Ratio
1	Seagate	st10000vx0004-1ze101	10	250	4.43	329	9,215	0.04
2	Seagate	st10000vn0004-1zd101	10	2,765	4.43	4,961	85,782	0.06
3	Seagate	st10000ne0004-1zf101	10	819	4.41	2,840	19,938	0.14
4	Seagate	st1000dm010-2ep102	1	442	4.43	488	2,968	0.16
5	Seagate	st10000ne0004-2gt11l	10	176	4.57	725	3,868	0.19
6	WDC	wdc wd2003fzex-00srla0	2	103	4.47	255	545	0.47
7	HGST	hgst hus722t2tala604	2	315	4.35	1,516	2,850	0.53
8	Seagate	st8000ne0004-1zf11g	8	800	4.43	8,265	14,946	0.55
9	WDC	wdc wd8003fryz-01jpdb1	8	661	4.59	55,795	77,148	0.72
10	HGST	hgst huh721212ale604	12	192	4.36	5,498	6,107	0.90
11	HGST	hgst hus726060ale610	6	271	4.48	23,297	25,868	0.90
12	WDC	wdc wd1005fbyz-01ycbb2	1	111	4.57	1,322	1,426	0.93
13	Seagate	st1000vn002-2ey102	1	697	4.45	8,474	6,819	1.24
14	WDC	wdc wd101kryz-01jpdb1	10	726	4.63	62,499	49,810	1.25
15	WDC	wdc wd2005fbyz-01ycbb2	2	478	4.65	6,653	4,762	1.40
16	Seagate	st8000vx0022-2ej112	8	382	4.52	10,208	7,189	1.42
17	Seagate	st4000nm0115-1yz107	4	262	4.45	31,351	21,756	1.44
18	Toshiba	toshiba hdwg11a	10	125	4.32	3,592	2,413	1.49
19	WDC	wdc wd60purz-85zufy1	6	246	4.41	10,549	6,970	1.51
20	HGST	hgst huh721010ale600	10	312	4.41	12,694	7,412	1.71
21	Seagate	st14000vn0008-2jg101	14	200	4.27	7,552	4,155	1.82
22	HGST	hgst hus728t8tale6l4	8	284	4.24	14,099	7,368	1.91
23	WDC	wdc wd60efrx-68l0bn1	6	5,126	4.46	203,116	104,943	1.94
24	WDC	wdc wd2002ffsx-68pf8n0	2	1,045	4.51	17,088	8,337	2.05
25	Seagate	st12000ne0007-2gt116	12	539	4.45	28,696	13,846	2.07
26	HGST	hgst huh721010ale604	10	315	4.37	26,029	11,980	2.17
27	HGST	hgst hdn721010ale604	10	294	4.64	18,727	8,435	2.22
28	WDC	wdc wd40ezrz-00gxcb0	4	679	4.41	21,626	9,535	2.27
29	WDC	wdc wd8003ffbx-68b9an0	8	933	4.36	72,529	30,574	2.37
30	WDC	wdc wd40purz-85ttdy0	4	809	4.42	41,872	16,976	2.47
31	WDC	wdc wd30ezrz-00gxcb0	3	139	4.56	6,616	2,633	2.51
32	Seagate	st4000vx000-2ag166	4	107	4.44	2,806	1,114	2.52
33	Seagate	st6000vn0041-2el11c	6	1,083	4.58	56,723	21,844	2.60
34	WDC	wdc wd100emaz-00wjta0	10	345	4.25	34,657	12,838	2.70
35	WDC	wdc wd4000f9yz-09n20l1	4	116	4.50	5,798	2,125	2.73
36	HGST	hgst hus726t4tala6l4	4	181	4.25	8,427	3,018	2.79
37	WDC	wdc wd100efax-68lhpn0	10	2,217	4.42	349,450	124,124	2.82
38	HGST	hgst huh721212ale600	12	265	4.35	30,883	10,927	2.83
39	WDC	wdc wd4003ffbx-68mu3n0	4	2,547	4.44	176,741	60,196	2.94
40	WDC	wdc wd40efrx-68n32n0	4	23,891	4.46	1,308,507	428,091	3.06
41	Toshiba	toshiba hdwn180	8	368	4.41	36,853	11,999	3.07
42	WDC	wdc wd30efrx-68n32n0	3	3,617	4.50	197,416	61,405	3.22
43	Seagate	st4000dm000-1f2168	4	109	4.45	4,548	1,407	3.23
44	WDC	wdc wd6002ffwx-68tz4n0	6	615	4.64	64,147	17,868	3.59
45	Seagate	st8000ne0021-2en112	8	238	4.56	20,683	5,615	3.68
46	WDC	wdc wd20purz-85gu6y0	2	350	4.33	10,323	2,794	3.69
47	WDC	wdc wd6003ffbx-68mu3n0	6	1,782	4.45	149,405	40,328	3.70
48	Toshiba	toshiba dt01aca200	2	480	4.51	20,597	5,208	3.95
49	WDC	wdc wd101kfbx-68r56n0	10	864	4.47	118,927	29,566	4.02
50	WDC	wdc wd121kryz-01w0rb0	12	540	4.62	77,793	19,137	4.07
51	WDC	wdc wd10purz-85u8xy0	1	129	4.43	6,717	1,640	4.10
52	Seagate	st6000nm0115-1yz110	6	888	4.47	94,069	22,845	4.12
53	Seagate	st2000ne0025-2fl101	2	503	4.50	23,567	5,666	4.16
54	HGST	hgst hdn724040ale640	4	224	4.54	17,453	4,087	4.27
55	WDC	wdc wd80emaz-00wjta0	8	496	4.42	49,521	11,579	4.28
56	WDC	wdc wd4002fyyz-01b7cb1	4	1,189	4.59	147,174	34,179	4.31
57	WDC	wdc wd20efrx-68euzn0	2	12,566	4.48	679,418	157,156	4.32
58	WDC	wdc wd80efax-68lhpn0	8	935	4.37	103,075	23,770	4.34
59	Seagate	st6000vn0033-2ee110	6	3,219	4.44	321,212	69,871	4.60
60	HGST	hgst hus726t6tale6l4	6	322	4.20	29,188	6,010	4.86
61	Seagate	st10000vn0004-2gs11l	10	664	4.65	119,913	24,373	4.92
62	HGST	hgst huh728080ale600	8	198	4.54	41,608	8,323	5.00
63	WDC	wdc wd6002fryz-01wd5b1	6	690	4.62	76,806	14,993	5.12
64	WDC	wdc wd8001ffwx-68j1un0	8	547	4.67	52,269	10,147	5.15
65	HGST	hgst hdn726040ale614	4	1,016	4.63	92,640	17,821	5.20
66	HGST	hgst hus726040ale610	4	130	4.59	13,211	2,495	5.30
67	Seagate	st12000nm0007-2a1101	12	652	4.37	177,372	31,684	5.60
68	HGST	hgst hdn726060ale614	6	522	4.61	96,880	16,819	5.76
69	HGST	hgst hus726t4tale6l4	4	209	4.26	19,024	3,185	5.97
70	Toshiba	toshiba dt01aca300	3	403	4.51	27,279	4,414	6.18
71	Seagate	st8000vn0022-2el112	8	5,905	4.46	1,087,817	175,748	6.19
72	WDC	wdc wd80efax-68knbn0	8	2,216	4.35	372,916	58,534	6.37
73	WDC	wdc wd30efrx-68euzn0	3	6,522	4.49	584,590	88,570	6.60
74	Seagate	st10000nm0016-1tt101	10	564	4.44	415,908	61,361	6.78
75	WDC	wdc wd4002ffwx-68tz4n0	4	583	4.64	74,497	10,874	6.85
76	Seagate	st4000ne0025-2ew107	4	1,728	4.48	204,073	25,800	7.91
77	WDC	wdc wd10efrx-68fytn0	1	3,955	4.48	207,517	26,079	7.96
78	WDC	wdc wd80ezaz-11tdba0	8	212	4.43	31,955	3,926	8.14
79	Seagate	st6000ne0023-2ex110	6	594	4.41	114,862	14,059	8.17
80	Seagate	st6000ne0021-2en11c	6	247	4.55	35,414	4,210	8.41
81	Seagate	st6000vx0023-2ef110	6	370	4.45	45,241	5,375	8.42
82	Toshiba	toshiba hdwd120	2	372	4.47	32,482	3,713	8.75
83	Toshiba	toshiba hdwd130	3	381	4.48	71,764	8,116	8.84
84	Seagate	st3000dm007-1wy10g	3	213	4.45	17,971	2,008	8.95
85	WDC	wdc wd4001ffsx-68jnun0	4	222	4.47	20,459	2,191	9.34
86	HGST	hgst hdn728080ale604	8	357	4.58	95,941	10,096	9.50
87	Seagate	st8000nm0055-1rm112	8	893	4.45	159,218	16,552	9.62
88	WDC	wdc wd4002fyyz-01b7cb0	4	205	4.52	22,738	2,257	10.07
89	Toshiba	toshiba hdwd110	1	145	4.42	10,423	1,015	10.27
90	WDC	wdc wd80efzx-68uw8n0	8	1,834	4.66	504,213	47,628	10.59
91	Hitachi	hitachi hus724030ale641	3	221	4.46	24,645	2,300	10.72
92	Toshiba	toshiba hdwn160	6	329	4.44	276,990	25,538	10.85
93	Seagate	st12000vn0007-2gs116	12	1,097	4.46	434,199	39,696	10.94
94	Seagate	st10000nm0086-2aa101	10	660	4.43	217,160	19,481	11.15
95	Toshiba	toshiba mg05aca800e	8	234	4.38	83,658	7,396	11.31
96	WDC	wdc wd3001ffsx-68jnun0	3	149	4.47	11,268	894	12.61
97	HGST	hgst hdn724030ale640	3	100	4.57	13,236	1,043	12.69
98	Toshiba	toshiba dt01aca100	1	217	4.42	15,176	1,148	13.22
99	Seagate	st4000nm0035-1v4107	4	1,018	4.48	325,120	23,182	14.02
100	Seagate	st2000nm0008-2f3100	2	428	4.53	68,901	4,736	14.55
101	WDC	wdc wd60efax-68shwn0	6	107	4.10	26,789	1,821	14.71
102	Seagate	st6000dm003-2cy186	6	286	4.44	83,494	5,115	16.32
103	Seagate	st1000nm0008-2f2100	1	157	4.47	25,466	1,521	16.74
104	Toshiba	toshiba mg04aca600e	6	258	4.51	109,339	6,446	16.96
105	Seagate	st8000dm004-2cx188	8	604	4.43	193,465	11,343	17.06
106	Seagate	st14000ne0008-2jk101	14	147	4.18	94,773	5,348	17.72
107	Seagate	st4000vx007-2dt166	4	646	4.51	196,320	11,039	17.78
108	Seagate	st4000dm005-2dp166	4	145	4.53	29,782	1,515	19.65
109	Toshiba	toshiba hdwe160	6	124	4.55	64,841	3,210	20.20
110	Toshiba	toshiba md04aca400	4	197	4.51	144,748	7,078	20.45
111	Seagate	st2000dm008-2fr102	2	291	4.25	69,211	2,685	25.77
112	Seagate	st4000vn008-2dr166	4	11,654	4.47	4,681,489	174,051	26.90
113	Seagate	st4000dm004-2cv104	4	1,263	4.44	347,954	11,904	29.23
114	Toshiba	toshiba mg04aca400n	4	281	4.44	62,260	2,011	30.96
115	Seagate	st8000as0002-1na17z	8	165	4.49	89,239	2,685	33.23
116	Toshiba	toshiba hdwq140	4	786	4.45	483,543	11,776	41.06
117	Seagate	st6000nm0024-1ht17z	6	143	4.55	76,186	1,620	47.04
118	Toshiba	toshiba mg04aca200e	2	129	4.41	78,111	1,021	76.49
119	Toshiba	toshiba mg04aca400e	4	281	4.38	382,158	3,392	112.66
120	Toshiba	toshiba hdwe140	4	153	4.43	149,924	1,258	119.21

NOTES: 

1. Cap TB refers to capacity in Terabytes for a given drive model

2. Avg POY refers to average power-on years for a given drive model

3. Total long latency read count is the sum of long latency reads for a given drive model

4. Total number of read commands is the sum of read commands for a given drive model

5. Long latency read ratio = total long latency read count / total number of read commands * 1,000,000

6. Drive models with outlier long latency read ratios are highlighted in bold

The drive models with low rank numbers (e.g., rank 1-10) have low long latency read ratios (i.e., only a few read commands result in long latency reads) and are generally expected to lag infrequently on reads. The drive models with high rank numbers (e.g., 111-120) have high long latency read ratios and are expected to lag more frequently on reads than drive models with low rank numbers. The drive models with the 10 highest (worst) rank numbers had exceptionally large long latency read ratios (1.5 IQR above Q3).

Neither the average power-on years, total number of read commands, nor capacity TB were significantly correlated (p > 0.05) with long latency read ratio. This means that these variables’ confounding effects on the drive model rankings were minimal.

Limitations

Before we conclude, we will acknowledge some limitations of the above ranking. First, we could not control for file size per command, which is a user-specific factor that may have influenced the drive ranking results, as we did not have the data to control for such a potential confound. Second, the drive rankings were based on drives with power-on years equivalent to 4-5 years, so we cannot generalize the rankings to drives older or younger than this. 

Summary

To recap, we compared several drive models and ranked them according to their long latency reads, normalized by the number of read commands issued to them. The rankings may offer some insight into how much lag may be felt by users when using certain drive models. The rankings may also be an indicator of potential drive model longevity, although we cannot say that long latency reads are by themselves an indicator of drive failure. Limitations were discussed.